Passive q-switched lasers and methods for operation and manufacture thereof

ABSTRACT

Systems and methods for imaging in the short wave infrared (SWIR), photodetectors with low dark current and associated circuits for reducing dark currents and methods for generating image information based on data of a photodetector array. A SWIR imaging system may include a pulsed illumination source operative to emit radiation pulses in the SWIR band towards a target resulting in reflected radiation from the target; (b) an imaging receiver including a plurality of Ge PDs operative to detect the reflected SWIR radiation and a controller, operative to control activation of the receiver for an integration time during which the accumulated dark current noise does not exceed the time independent readout noise.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/266,142 filed Feb. 5, 2021, which was a 371 application frominternational patent application No. PCT/IB2020/060011 filed Oct. 24,2020, and is related to and claims priority from U.S. patent applicationSer. No. 16/662,665 filed Oct. 24, 2019, No. 63/075,426 filed Sep. 8,2020, No. 63/093,945 filed Oct. 20, 2020 and No. 63/094,913 filed Oct.22, 2020, all of which are incorporated herein by reference in theirentirety.

FIELD

The disclosure relates to photonic systems, methods, and computerprogram products. More specifically, the disclosure relates toelectro-optics and lasers used in infrared (IR) photonics.

BACKGROUND

Photodetecting devices such as photodetector arrays (also referred to as“photosensor arrays”) include a multitude of photosites, each includingone or more photodiodes for detecting impinging light and capacitancefor storing charge provided by the photodiode. The capacitance may beimplemented as a dedicated capacitor and/or using parasitic capacitanceof the photodiode, transistors, and/or other components of the PS.Henceforth in this description and for simplicity, the term“photodetecting device” is often replaced with the acronym “PDD”, theterm “photodetector array” is often replaced with the acronym “PDA”, andthe term “photodiode” is often replaced with the acronym “PD”.

The term “photosite” pertains to a single sensor element of an array ofsensors (also referred to “sensel”, as in a portmanteau of the words“sensor” and “cell” or “sensor” and “element”), and is also referred toas “sensor element”, “photosensor element”, “photodetector element”, andso on. Hereinbelow, “photosite” is often replaced with the acronym “PS”.Each PS may include one or more PDs (e.g., if color filter array isimplemented, PDs which detect light of different parts of the spectrummay optionally be collectively referred to as single PS). The PS mayalso include some circuitry or additional components in addition to thePD.

Dark current is a well-known phenomenon, and when referring to PDs itpertains to an electric current that flows through the PD even when nophotons are entering the device. Dark current in PDs may result fromrandom generation of electrons and holes within a depletion region ofthe PD.

In some cases, there is a need to provide photosites with photodiodescharacterized by a relatively high dark current, while implementingcapacitors of limited size. In some cases, there is a need to providePSs with PDs characterized by a relatively high dark current whilereducing effects of the dark current on an output detection signal. InPSs characterized by high dark current accumulation, there is a needfor, and it would be advantageous to overcome detrimental effects ofdark current on electrooptical systems. Henceforth and for simplicity,the term “electrooptical” may be replaced with the acronym “EO”.

Short-wave infrared (SWIR) imaging enables a range of applications thatare difficult to perform using imaging of visible light. Applicationsinclude electronic board inspection, solar cell inspection, produceinspection, gated imaging, identifying and sorting, surveillance,anti-counterfeiting, process quality control, and much more. Manyexisting InGaAs-based SWIR imaging systems are expensive to fabricate,and currently suffer from limited manufacturing capacity.

It would therefore be advantageous to be able to provide SWIR imagingsystems using more cost-effective photoreceivers based on PDs that aremore easily integrated into the surrounding electronics.

SUMMARY

According to an aspect of the disclosure, there is provided an activeSWIR imaging system that includes: a pulsed illumination sourceoperative to emit SWIR radiation pulses towards a target, the radiationpulses impinging on the target resulting in reflected SWIR radiationpulses reflected from the target; an imaging receiver comprising aplurality of Germanium (Ge) PDs operative to detect the reflected SWIRradiation, wherein the imaging receiver produces for each Ge PD arespective detection signal representative of the reflected SWIRradiation impinging on the respective Ge PD, a dark current that islarger than 50 μA/cm², time dependent dark current noise and timeindependent readout noise; and a controller, operative to controlactivation of the imaging receiver for an integration time during whichan accumulated dark current noise does not exceed the time independentreadout noise.

According to an aspect of the disclosure, there is disclosed a methodfor generating SWIR images of objects in a field of view (FOV) of an EOsystem, the method including: emitting at least one illumination pulsetoward the FOV, resulting in SWIR radiation reflecting from at least onetarget; triggering initiation of continuous signal acquisition by animaging receiver that includes a plurality of Ge PDs operative to detectthe reflected SWIR radiation; collecting for each of the plurality of GePDs, as a result of the triggering, charge resulting from at least theimpinging of the SWIR reflection radiation on the respective Ge PD, darkcurrent that is larger than 50 μA/cm², integration-time dependent darkcurrent noise, and integration-time independent readout noise;triggering ceasing of the collection of the charge when the amount ofcharge collected as a result of dark current noise is still lower thanthe amount of charge collected as a result of the integration-timeindependent readout noise; and generating an image of the FOV based onthe levels of charge collected by each of the plurality of Ge PDs.

According to an aspect of the disclosure, there is disclosed a SWIRoptical system, the SWIR system that includes a passively Q-switchedlaser (also referred to herein as “P-QS laser”) that includes: a gainmedium including a gain medium crystalline (GMC) material that isceramic neodymium-doped yttrium aluminum garnet (Nd:YAG); a saturableabsorber (SA) rigidly connected to the gain medium, the SA including aceramic SA crystalline material selected from a group of doped ceramicmaterials consisting of: V³⁺:YAG and two-valence Cobalt-dopedcrystalline materials; and an optical cavity within which the gainmedium and the SA are positioned, the optical cavity including a highreflectivity mirror and an output coupler.

Henceforth in this description and for simplicity, the term “saturableabsorber” is often replaced with the acronym “SA”.

According to an aspect of the disclosure, there is disclosed a SWIRoptical system, the SWIR system including a P-QS laser that includes: again medium including a GMC material that is ceramic Nd:YAG, a SArigidly connected to the gain medium, the SA including a ceramic SAcrystalline material selected from a group of doped ceramic materialsconsisting of: V³⁺:YAG and two-valence Cobalt-doped crystallinematerials; and an optical cavity within which the gain medium and the SAare positioned, the optical cavity including a high reflectivity mirrorand an output coupler.

According to an aspect of the disclosure, there is disclosed a SWIRoptical system, that includes a P-QS laser that includes: a gain mediumincluding a ceramic GMC material that is ceramic neodymium-dopedrare-earth element crystal; a SA rigidly connected to the gain medium,the SA including a ceramic SA crystalline material selected from a groupof doped crystalline materials consisting of: V³⁺:YAG and Cobalt-dopedcrystalline materials; and an optical cavity within which the gainmedium and the SA are positioned, the optical cavity including a highreflectivity mirror and an output coupler.

According to an aspect of the disclosure, there is disclosed a methodfor manufacturing parts for a P-QS laser, the method including:inserting into a first mold at least one first powder; compacting the atleast one first powder in the first mold to yield a first green body;inserting into a second mold at least one second powder different thanthe at least one first powder; compacting the at least one second powderin the second mold, thereby yielding a second green body; heating thefirst green body to yield a first crystalline material; heating thesecond green body to yield a second crystalline material; and connectingthe second crystalline material to the first crystalline material. Insuch a case, one crystalline material out of the first crystallinematerial and the second crystalline material is a neodymium-dopedcrystalline material and is a gain medium for the P-QS laser, andwherein the other crystalline material out of the first crystallinematerial and the second crystalline material is a SA for the P-QS laserand is selected from a group of crystalline materials consisting of aneodymium-doped crystalline material, and a doped crystalline material,the latter selected from the group of doped crystalline materialsconsisting of: V³⁺:YAG and cobalt-doped crystalline materials. Also, insuch a case, at least one of the gain medium and the SA is a ceramiccrystalline material.

According to an aspect of the disclosure, there is disclosed a PDD thatincludes: an active PS including an active PD; a reference PS includinga reference PD; a first voltage controlled current circuit consisting ofa voltage-controlled current source or a voltage-controlled currentsink, the first voltage controlled current circuit connected to theactive PD; and control-voltage generating circuitry connected to theactive voltage controlled current circuit and to the reference PS andused to provide to the voltage controlled current circuit a controlvoltage having a voltage level that is responsive to dark current of thereference PD, to reduce an effect of dark current of the active PD on anoutput of the active PS.

According to an aspect of the disclosure, there is disclosed a methodfor reducing effects of dark current in a PDD, the method including:when the PDD operates in a first temperature, determining a firstcontrol voltage based on dark current of at least one reference PD ofthe PDD; providing the first control voltage to a first voltagecontrolled current circuit that is connected to at least one active PDof an active PS of the PDD, thereby causing the first voltage controlledcurrent circuit to impose a first dark-current countering current in theactive PS; generating by the active PD a first detection current inresponse to light impinging of the active PD originating in an object ina field of view of the PDD, and to dark current generated by the activePD; and outputting by the active PS a first detection signal whosemagnitude is smaller than the first detection current in response to thefirst detection current and to the first dark-current counteringcurrent, thereby compensating effect of dark current on the firstdetection signal; and when the PDD operates in a second temperature thatis higher than the first temperature by at least 10° C., determining asecond control voltage based on dark current of at least one referencePD of the PDD; providing the second control voltage to the first voltagecontrolled current circuit, thereby causing the first voltage controlledcurrent circuit to impose a second dark-current countering current inthe active PS; generating by the active PD a second detection current inresponse to light impinging of the active PD originating in the object,and to dark current generated by the active PD; and outputting by theactive PS a second detection signal whose magnitude is smaller than thesecond detection current in response to the second detection current andto the second dark-current countering current, thereby compensatingeffect of dark current on the second detection signal. A magnitude ofthe second dark-current countering current in such a case larger than amagnitude of the first dark-current countering current by a factor of atleast two.

According to an aspect of the disclosure, there is disclosed a methodfor testing a PDD, comprising: providing a first voltage to a firstinput of an amplifier of a control-voltage generating circuitry, whereinthe second input of the amplifier is connected to a reference PD and toa second current circuit which supplies current in a level governed inresponse to an output voltage of the amplifier; thereby causing theamplifier to generate a first control voltage for a first currentcircuit of a PS of the PDD; reading a first output signal of the PSgenerated by the PS in response to current generated by the firstcurrent circuit and to a PD of the PS; providing to the first input ofthe amplifier a second voltage that is different than the first inputvoltage, thereby causing the amplifier to generate a second controlvoltage for the first current circuit; reading a second output signal ofthe PS generated by the PS in response to current generated by the firstcurrent circuit and to a PD of the PS; and based on the first outputsignal and on the second output signal, determining a defectivity stateof a detection path of the PDD, the detection path including the PS andreadout circuitry associated with the PS.

According to an aspect of the disclosure, there is disclosed a systemfor generating images, comprising a processor configured to: receivefrom a PDA multiple detection results of an object including a highreflectivity surface surrounded by low reflectivity surfaces on allsides, the multiple detection results including first frame informationof the object detected by the PDA during a first frame exposure time andsecond frame information of the object detected by the PDA during asecond frame exposure time that is longer than the first frame exposuretime; process the first frame information based on the first frameexposure time to provide a first image that includes a bright regionrepresenting the high reflectivity surface, surrounded by a darkbackground representing the low reflectivity surfaces; and process thesecond frame information based on the second frame exposure time toprovide a second image that includes a dark background without a brightregion.

According to an aspect of the disclosure, there is disclosed a systemfor generating images comprising a processor configured to: receive froma PDA multiple detection results of an object including a highreflectivity surface surrounded by low reflectivity surfaces on allsides, the multiple detection results including first frame informationof the object detected by the PDA during a first frame exposure time andsecond frame information of the object detected by the PDA during asecond frame exposure time that is longer than the first frame exposuretime; process the first frame information based on the first frameexposure time to provide a first image that includes a bright regionrepresenting the high reflectivity surface, surrounded by a darkbackground representing the low reflectivity surfaces; and process thesecond frame information based on the second frame exposure time toprovide a second image that includes a dark background without a brightregion.

According to an aspect of the disclosure, there is disclosed a methodfor generating image information based on data of a PDA comprising:receiving from a PDA first frame information of a low reflectivitytarget that includes a high reflectivity area, indicative of lightintensities of different parts of the target detected by the PDA duringa first frame exposure time; processing the first frame informationbased on the first frame exposure time to provide a first image thatincludes a bright region surrounded by a dark background; receiving fromthe PDA second frame information of the low reflectivity target thatincludes the high reflectivity area, indicative of light intensities ofthe different parts of the target detected by the PDA during a secondframe exposure time that is longer than the first frame exposure time;and processing the second frame information based on the second frameexposure time to provide a second image that includes a dark backgroundwithout a bright region.

According to an aspect of the disclosure, there is disclosed anon-transitory computer-readable medium for generating image informationbased on data of a PDA, including instructions stored thereon, that whenexecuted on a processor, perform the steps of: receiving from a PDAfirst frame information of a black target that includes a white area,indicative of light intensities of different parts of the targetdetected by the PDA during a first frame exposure time; processing thefirst frame information based on the first frame exposure time toprovide a first image that includes a bright region surrounded by a darkbackground; receiving from the PDA second frame information of the blacktarget that includes the white area, indicative light intensities of thedifferent parts of the target detected by the PDA during a second frameexposure time that is longer than the first frame exposure time; andprocessing the second frame information based on the second frameexposure time to provide a second image that includes a dark backgroundwithout a bright region.

According to an aspect of the disclosure, there is disclosed an EOsystem with dynamic PS usability assessment, the system comprising: aPDA including a plurality of photosites (PS), each PS operative tooutput detection signals at different frames, the detection signaloutput for a frame by the respective PS being indicative of amount oflight impinging on the respective PS during a respective frame; ausability filtering module, operative to determine for each PS that thePS is unusable based on a first frame exposure time, and to laterdetermine that the PS is usable based on a second frame exposure timethat is shorter than the first frame exposure time; and a processoroperative to generate images based on frame detection levels of theplurality of PSs. The processor is configured to: (i) exclude, whengenerating a first image based on first frame detection levels, a firstdetection signal of a filtered PS that was determined by the usabilityfiltering module as unusable for the first image, and (ii) include, whengenerating a second image based on second frame detection levelscaptured by the PDA after the capturing of the first frame detectionlevels, a second detection signal of the filtered PS that was determinedby the usability filtering module as usable for the second image.

According to an aspect of the disclosure, there is disclosed a methodfor generating image information based on data of a PDA, comprising:receiving first frame information including for each out of a pluralityof PSs of the PDA a first frame detection level indicative of anintensity of light detected by the respective PS during a first frameexposure time; based on the first frame exposure time, identifying outof the plurality of PSs of the PDD: a first group of usable PSsincluding a first PS, a second PS, and a third PS, and a first group ofunusable PSs including a fourth PS; generating a first image based onthe first frame detection levels of the first group of usable PSs,disregarding first frame detection levels of the first group of unusablePSs; determining, after receiving the first frame information, a secondframe exposure time that is longer than the first frame exposure time;receiving second frame information including for each of the pluralityof PSs of the PDA a second frame detection level indicative of anintensity of light detected by the respective PS during a second frameexposure time; based on the second frame exposure time, identifying outof the plurality of PSs of the PDD: a second group of usable PSsincluding the first PS, and a second group of unusable PSs including thesecond PS, and the third PS, and the fourth PS; (g) generating a secondimage based on the second frame detection levels of the second group ofusable PSs, disregarding second frame detection levels of the secondgroup of unusable PSs; determining, after receiving the second frameinformation, a third frame exposure time that is longer than the firstframe exposure time and shorter than the second frame exposure time;receiving third frame information including for each of the plurality ofPSs of the PDA a third frame detection level indicative of an intensityof light detected by the respective PS during a third frame exposuretime; based on the third frame exposure time, identifying out of theplurality of PSs of the PDD: a third group of usable PSs including thefirst PS and the second PS, and a third group of unusable PSs includingthe third PS and the fourth PS; and (k) generating a third image basedon the third frame detection levels of the third group of usable PSs,disregarding third frame detection levels of the third group of unusablePSs.

According to an aspect of the disclosure, there is disclosed anon-transitory computer-readable medium for generating image informationbased on data of a PDA, including instructions stored thereon, that whenexecuted on a processor, perform the steps of: receiving first frameinformation including for each out of a plurality of PSs of the PDA afirst frame detection level indicative of an intensity of light detectedby the respective PS during a first frame exposure time; based on thefirst frame exposure time, identifying out of the plurality of PSs ofthe PDD: a first group of usable PSs including a first PS, a second PS,and a third PS, and a first group of unusable PSs including a fourth PS;generating a first image based on the first frame detection levels ofthe first group of usable PSs, disregarding first frame detection levelsof the first group of unusable PSs; determining, after receiving thefirst frame information, a second frame exposure time that is longerthan the first frame exposure time; receiving second frame informationincluding for each of the plurality of PSs of the PDA a second framedetection level indicative of an intensity of light detected by therespective PS during a second frame exposure time; based on the secondframe exposure time, identifying out of the plurality of PSs of the PDD:a second group of usable PSs including the first PS, and a second groupof unusable PSs including the second PS, and the third PS, and thefourth PS; generating a second image based on the second frame detectionlevels of the second group of usable PSs, disregarding second framedetection levels of the second group of unusable PSs; determining, afterreceiving the second frame information, a third frame exposure time thatis longer than the first frame exposure time and shorter than the secondframe exposure time; receiving third frame information including foreach of the plurality of PSs of the PDA a third frame detection levelindicative of an intensity of light detected by the respective PS duringa third frame exposure time; based on the third frame exposure time,identifying out of the plurality of PSs of the PDD: a third group ofusable PSs including the first PS and the second PS, and a third groupof unusable PSs including the third PS and the fourth PS; and generatinga third image based on the third frame detection levels of the thirdgroup of usable PSs, disregarding third frame detection levels of thethird group of unusable PSs.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples of embodiments disclosed herein are describedbelow with reference to figures attached hereto that are listedfollowing this paragraph. Identical structures, elements or parts thatappear in more than one figure may be labeled with a same numeral in allthe figures in which they appear. The drawings and descriptions aremeant to illuminate and clarify embodiments disclosed herein, and shouldnot be considered limiting in any way. All the drawings show devices orflow charts in accordance with examples of the presently disclosedsubject matter. In the drawings:

FIGS. 1A, 1B and 1C are schematic block diagrams illustrating activeSWIR imaging systems;

FIG. 2 is an exemplary graph illustrating relative magnitudes of noisepower after different durations of integration times in a SWIR imagingsystem;

FIGS. 3A, 3B and 3C show respectively a flowchart and schematic drawingsof a method of operation of an active SWIR imaging system according tosome embodiments;

FIGS. 4A, 4B and 4C show respectively a flowchart and schematic drawingsof an exemplary method of operation of an active SWIR imaging system;

FIG. 5 is a flowchart illustrating a method for generating SWIR imagesof objects in a FOV of an EO system;

FIG. 6 is a schematic functional block diagram illustrating an exampleof a SWIR optical system;

FIGS. 7A, 7B and 7C are schematic functional block diagrams illustratingexamples of P-QS laser;

FIGS. 8 and 9 are schematic functional diagrams illustrating a SWIRoptical system;

FIG. 10 is a schematic functional block diagram illustrating an exampleof a SWIR optical system;

FIGS. 11A, 11B and 11C show respectively a flow chart illustrating anexample of a method for manufacturing parts for a P-QS laser, andconceptual timelines for the execution of the method;

FIG. 12A shows schematically a PS that includes a PD controlled by avoltage-controlled current source;

FIG. 12B shows schematically a PS that includes a PD controlled by avoltage-controlled current source in a “3T” structure;

FIGS. 13A and 13B show a PDD including a PS and circuitry operative toreduce effects of dark current;

FIG. 13C shows a PDD comprising a plurality of PSs and circuitryoperative to reduce effects of dark current;

FIG. 14 shows an exemplary PD I-V curve and possible operationalvoltages for a PDD;

FIG. 15 shows a control-voltage generating circuitry that is connectedto a plurality of reference photosites;

FIGS. 16A and 16B show PDDs which comprise an array of PSs and referencecircuitry based on a plurality of PDs;

FIGS. 17 and 18 show PDDs, each comprising a PS and circuitry operativeto reduce effects of dark current;

FIG. 19 illustrates a PDD that includes optics, a processor, andadditional components;

FIG. 20 is a flow chart illustrating a method for compensating for darkcurrent in a photodetector;

FIG. 21 is a flow chart illustrating a method for compensating for darkcurrent in a photodetector;

FIG. 22 is a flow chart illustrating a method for testing aphotodetector;

FIG. 23 illustrates an EO system according to some embodiments;

FIG. 24 illustrates an example of a method for generating imageinformation based on data of a PDA;

FIGS. 25 and 26 show respectively a flow chart illustrating a method forgenerating a model for PDA operation in different frame exposure times,and a graphical representation of execution of that method for differentframes which are taken of the same scene in different frame exposuretimes;

FIG. 27 is a flow chart illustrating an example of a method forgenerating images based on different subsets of PSs in differentoperational conditions;

FIGS. 28A and 28 B illustrate an EO system and exemplary target objects;

FIG. 29 is a flow chart illustrating a method for generating imageinformation based on data of a PDA;

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, numerous specific details are setforth to provide a thorough understanding of the disclosure. However, itwill be understood by those skilled in the art that the presentdisclosure may be practiced without these specific details. In otherinstances, well-known methods, procedures, and components have not beendescribed in detail so as not to obscure the present disclosure.

In the drawings and descriptions set forth, identical reference numeralsindicate those components that are common to different embodiments orconfigurations.

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions utilizing terms such as “processing”, “calculating”,“computing”, “determining”, “generating”, “setting”, “configuring”,“selecting”, “defining”, or the like, include action and/or processes ofa computer that manipulate and/or transform data into other data, saiddata represented as physical quantities, e.g. such as electronicquantities, and/or said data representing the physical objects.

The terms “computer”, “processor”, and “controller” should beexpansively construed to cover any kind of electronic device with dataprocessing capabilities, including, by way of non-limiting example, apersonal computer, a server, a computing system, a communication device,a processor (e.g. digital signal processor (DSP), a microcontroller, afield programmable gate array (FPGA), an application specific integratedcircuit, etc.), any other electronic computing device, and or anycombination thereof.

The operations in accordance with the teachings herein may be performedby a computer specially constructed for the desired purposes or by ageneral purpose computer specially configured for the desired purpose bya computer program stored in a computer readable storage medium.

As used herein, the phrase “for example,” “such as”, “for instance” andvariants thereof describe non-limiting embodiments of the presentlydisclosed subject matter. Reference in the specification to “one case”,“some cases”, “other cases” or variants thereof means that a particularfeature, structure or characteristic described in connection with theembodiment(s) is included in at least one embodiment of the presentlydisclosed subject matter. Thus the appearance of the phrase “one case”,“some cases”, “other cases” or variants thereof does not necessarilyrefer to the same embodiment(s).

It is appreciated that certain features of the presently disclosedsubject matter, which are, for clarity, described in the context ofseparate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features of the presently disclosedsubject matter, which are, for brevity, described in the context of asingle embodiment, may also be provided separately or in any suitablesub-combination.

In embodiments of the presently disclosed subject matter one or morestages or steps illustrated in the figures may be executed in adifferent order and/or one or more groups of stages may be executedsimultaneously and vice versa. The figures illustrate a generalschematic of the system architecture in accordance with an embodiment ofthe presently disclosed subject matter. Each module in the figures canbe made up of any combination of software, hardware and/or firmware thatperforms the functions as defined and explained herein. The modules inthe figures may be centralized in one location or dispersed over morethan one location.

Any reference in the specification to a method should be applied mutatismutandis to a system capable of executing the method and should beapplied mutatis mutandis to a non-transitory computer readable mediumthat stores instructions that once executed by a computer result in theexecution of the method.

Any reference in the specification to a system should be applied mutatismutandis to a method that may be executed by the system and should beapplied mutatis mutandis to a non-transitory computer readable mediumthat stores instructions that may be executed by the system.

Any reference in the specification to a non-transitory computer readablemedium or similar terms should be applied mutatis mutandis to a systemcapable of executing the instructions stored in the non-transitorycomputer readable medium and should be applied mutatis mutandis tomethod that may be executed by a computer that reads the instructionsstored in the non-transitory computer readable medium.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. The materials, methods, andexamples provided herein are illustrative only and not intended to belimiting.

Implementation of the method and system of the present disclosureinvolves performing or completing certain selected tasks or stepsmanually, automatically, or a combination thereof. Moreover, accordingto actual instrumentation and equipment of preferred embodiments of themethod and system of the present disclosure, several selected stepscould be implemented by hardware or by software on any operating systemof any firmware or a combination thereof. For example, as hardware,selected steps of the disclosure could be implemented as a chip or acircuit. As software, selected steps of the disclosure could beimplemented as a plurality of software instructions being executed by acomputer using any suitable operating system. In any case, selectedsteps of the method and system of the disclosure could be described asbeing performed by a data processor, such as a computing platform forexecuting a plurality of instructions.

FIGS. 1A, 1B, and 1C are schematic block diagrams illustratingrespectively active SWIR imaging systems 100, 100′ and 100″, inaccordance with examples of the presently disclosed subject matter.

As used herein, an “active” imaging system is operative to detect lightreaching the system from its field-of-view (FOV), detect it by animaging receiver that includes a plurality of PDs, and process thedetection signals to provide one or more images of the field of view orpart thereof. The term “image” refers to a digital representation of ascene detected by the imaging system, which stores a color value foreach picture element (pixel) in the image, each pixel color representinglight arriving to the imaging system from a different part of thefield-of-view (e.g., a 0.02° by 0.02° part of the FOV, depending onreceiver optics). It is noted that optionally, the imaging system may befurther operative to generate other representations of objects or lightin the FOV (e.g., a depths map, 3D model, polygon mesh), but the term“image” refers to two-dimensional (2D) image with no depth data.

System 100 comprises an illumination source (IS) 102 operative to emitradiation pulses in the SWIR band towards one or more targets 104,resulting in reflected radiation from the target reflected back in thedirection of system 100. In FIG. 1A, outgoing illumination is denoted106 and illumination reflected toward system 100 is denoted 108. Partsof the emitted radiation may also be reflected in other directions,deflected, or absorbed by the target. The term “target” refers to anyobject in the FOV of the imaging sensor, such as solids, liquid,flexible, and rigid objects. Some non-limiting examples of such objectsinclude vehicles, roads, people, animals, plants, buildings,electronics, clouds, microscopic samples, items during manufacturing,and so on. Any suitable type of illumination source 102 may be used,such as one or more lasers, one or more light emitting diodes (LEDs),one or more incidence flashlights, any combination of the above, and soon. As discussed below in greater detail, illumination source 102 mayoptionally include one or more active lasers, or one or more P-QSlasers.

System 100 also includes at least one imaging receiver (or simply“receiver”) 110 that includes a plurality of Germanium (Ge) PDsoperative to detect the reflected SWIR radiation. Receiver produces foreach of the plurality of Ge PDs an electrical signal that isrepresentative of the amount of impinging SWIR light within itsdetectable spectral range. That amount includes the amount of reflectedSWIR radiation pulse light from the target, and may also includeadditional SWIR light (e.g., arriving from the sun or from externallight sources).

The term “Ge PD” pertains to any PD in which light induced excitation ofelectrons (later detectable as a photocurrent) occurs within the Ge,within a Ge alloy (e.g., SiGe), or at the interface between Ge (or Gealloy) and another material (e.g., silicon, SiGe). Specifically, theterm “Ge PD” pertains both to pure Ge PDs and to Ge-silicon PDs. When GePDs which include both Ge and silicon are used, different concentrationof geranium may be used. For example, the relative portion of Ge in theGe PDs (whether alloyed with silicon or adjacent to it) may range from5% to 99%. For example, the relative portion of Ge in the Ge PDs may bebetween 15% and 40%. It is noted that materials other than silicon mayalso be part of the Ge PD, such as aluminum, nickel, silicide, or anyother suitable material. In some implementation of the disclosure, theGe PDs may be pure Ge PDs (including more than 99.0% Ge).

It is noted that the receiver may be implemented as a PDA manufacturedon a single chip. Any of the PD arrays discussed throughout the presentdisclosure may be used as receiver 110. The Ge PDs may be arranged inany suitable arrangement, such as a rectangular matrix (straight rowsand straight columns of Ge PD), honeycomb tiling, and even irregularconfigurations. Preferably, the number of Ge PDs in the receiver allowsgeneration of high-resolution image. For example, the number of PDs maybe in the order of scale of 1 Megapixel, 10 Megapixel, or more.

In some embodiments, receiver 110 has the following specifications:

a. HFOV (horizontal field of view) [m]: 60 b. WD (working distance) [m]:150 c. Pixel Size [um]: 10 d. Resolution (on Obj.) [mm]: 58 e. Pixels #[H]: 1,050 f. Pixels # [V]: 1112 g. Aspect Ratio: 3:1 h. View Angle[rad]: 0.4 i. Reflectivity of the target [%]: 10% j. Collection (theratio of collected photons to emitted photons assuming targetreflectivity of 100% and assuming Lambertian reflectance): 3e⁻⁹.

In addition to the impinging SWIR light as discussed above, theelectrical signal produced by each of the Ge PDs is also representativeof:

a. Readout noise, which is random, and its magnitude is independent (orsubstantially independent) on the integration time. Example of suchnoise includes Nyquist Johnson noise (also referred to as thermal noiseor kTC noise). The readout process may also introduce a DC component tothe signal, in addition to the statistical component, but the term“readout noise” pertains to the random component of the signalintroduced by the readout process.

b. Dark current noise, which is random and accumulating over theintegration time (i.e., it is integration-time dependent). The darkcurrent also introduces in addition to the statistical component a DCcomponent to the signal (which may or may not be eliminated, e.g., asdiscussed with respect to FIGS. 12A through 22), but the term “darkcurrent noise” pertains to the random component of the signalaccumulated over the integration time resulting from the dark current.

Some Ge PDs, and especially some PDs that combine Ge with anothermaterial (such as silicon, for example) are characterized by arelatively high level of dark current. For example, the dark current ofGe PDs may be larger than 50 μA/cm² (pertaining to a surface area of thePD) and even larger (e.g., larger than 100 μA/cm², larger than 200μA/cm², or larger than 500 μA/cm²). Depending on the surface area of thePD, such levels of dark current may be translated to 50 picoampere (pA)per Ge PD or more (e.g., more than 100 μA per Ge PD, more than 200 μAper Ge PD, more than 500 μA per Ge PD, or more than 2 nA per Ge PD). Itis noted that different sizes of PDs may be used, such as about 10 mm²,about 50 mm², about 100 mm², about 500 mm²). It is noted that differentmagnitudes of dark current may be generated by the Ge PDs when the GePDs are subject to different levels of nonzero bias (which induce oneach of the plurality of Ge PDs a dark current that is, for example,larger than 50 picoampere).

System 100 further comprises a controller 112, which controls operationof receiver 110 (and optionally also of illumination source (IS) 102and/or other components) and an image processor 114. Controller 112 istherefore configured to control activation of receiver 110 for arelatively short integration time, such that to limit the effect ofaccumulation of dark current noise on the quality of the signal. Forexample, controller 112 may be operative to control activation ofreceiver 110 for an integration time during which the accumulated darkcurrent noise does not exceed the integration-time independent readoutnoise.

Refer now to FIG. 2, which is an exemplary graph illustrating relativemagnitudes of noise power after different durations of integrationtimes, in accordance with examples of the presently disclosed subjectmatter. For a given laser pulse energy, the signal to noise ratio (SNR)is mostly dictated by the noise level that includes the dark currentnoise (noise of the dark photocurrent) and thermal noise (also referredto as kTC noise). As shown in the exemplary graph of FIG. 2, either ofthe dark current noise or the thermal noise are dominant in effectingthe SNR of the electric signal of the PD, depending on the integrationtime of Ge-based receiver 110. Since controller 112 limits theactivation time of the Ge photodetector for a relatively short time(within the range designated as “A” in FIG. 2), not many electronsoriginating from dark current noise are collected and the SNR istherefore improved and is thus affected mainly by the thermal noise. Fora longer receiver integration time, the noise originating from the darkcurrent of the Ge photodetector becomes dominant over the thermal noisein affecting the receiver SNR, resulting in degraded receiverperformance. It is noted that the graph of FIG. 2 is merelyillustrative, and that accumulation of dark current noise over time isusually increasing with the square root of the time E_(noise)∝√{squareroot over (T_(integration))}. (alternatively, consider the y-axis asdrawn on a matching non-linear polynomial scale). Also, the axes do notcross each other at zero integration time (in which case the accumulateddark current noise is zero).

Reverting to system 100, it is noted that controller 112 may controlactivation of receiver 110 for even shorter integration times (e.g.,integration times during which the accumulated dark current noise doesnot exceed half of the readout noise, or a quarter of the readoutnoise). It is noted that unless specifically desired, limiting theintegration time to very low levels limits the amount of light inducedsignals which may be detected, and worsens the SNR with respect to thethermal noise. It is noted that the level of thermal noise in readoutcircuitries suitable for reading of noisy signals (which requirecollection of relatively high signal level) introduces non-negligiblereadout noise, which may significantly deteriorate the SNR.

In some implementations, somewhat longer integration times may beapplied by controller 112 (e.g., integration times during which theaccumulated dark current noise does not exceed twice the readout noise,or ×1.5 of the readout noise).

Exemplary embodiments disclosed herein relate to systems and methods forhigh SNR active SWIR imaging using receivers including Ge based PDs. Themajor advantage of Ge receiver technology vs. InGaAs technology is thecompatibility with CMOS processes, allowing manufacture of the receiveras part of a CMOS production line. For example, Ge PDs can be integratedinto CMOS processes by growing Ge epilayers on a silicon (Si) substrate,such as in Si photonics. Ge PDs are also therefore more cost effectivethan equivalent InGaAs PDs.

To utilize Ge PDs, an exemplary system disclosed herein is adapted toovercome the limitation of the relatively high dark current of Gediodes, typically in the ˜50 uA/cm{circumflex over ( )}2 range. Thedark-current issue is overcome by use of active imaging having acombination of short capture time and high-power laser pulses.

The utilization of Ge PDs—especially but not limited to ones which arefabricated using CMOS processes—is a much cheaper solution for uncooledSWIR imaging than InGaAs technology. Unlike many prior art imagingsystems, active imaging system 100 includes a pulsed illumination sourcewith a short illumination duration (for example, below 10, e.g., 1-1000μS) and high peak power. This despite the drawbacks of such pulsed lightsources (e.g. illumination non-uniformity, more complex readoutcircuitry which may introduce higher levels of readout noise) and thedrawbacks of shorter integration time (e.g., the inability to capture awide range of distances at a single acquisition cycle). In the followingdescription, several ways are discussed for overcoming such drawbacks toprovide effective imaging systems.

Reference is now made to FIGS. 1B and 1C that illustrate schematicallyother SWIR imaging systems according to some embodiments and numbered100′ and 100″. Like system 100, system 100′ comprises an activeillumination source 102A and receiver 110. In some embodiments, imagingsystems 100, 100′ and 100″ further comprise controller 112 and imageprocessor 114. In some embodiments, processing of the output of receiver110 may be performed by image processor 114 and additionally oralternatively by an external image processor (not shown). Imagingsystems 100′ and 100″ may be variations of imaging system 100. Anycomponent or functionality discussed with respect to system 100 may beimplemented in any of systems 100′ and 100″, and vice versa.

Controller 112 is a computing device. In some embodiments, the functionsof controller 112 are provided within illumination source 102 andreceiver 110, and controller 112 is not required as a separatecomponent. In some embodiments, the control of imaging systems 100′ and100″ is performed by controller 112, illumination source 102 andreceiver 110 acting together. Additionally or alternatively, in someembodiments, control of imaging systems 100′ and 100″ may be performed(or performed supplementally) by an external controller such as avehicle Electronic Control Unit (ECU) 120 (which may belong to a vehiclein which the imaging system is installed).

Illumination source 102 is configured to emit a light pulse 106 in theinfrared (IR) region of the electromagnetic spectrum. More particularly,light pulse 106 is in the SWIR spectral band including wavelengths in arange from approximately 1.3 μm to 3.0 μm.

In some embodiments, such as shown in FIG. 1B, the illumination source(now marked 102A) is an active Q-switch laser (or “actively Q-switched”laser) that includes a gain medium 122, a pump 124, mirrors (not shown)and an active QS element 126A. In some embodiments, QS element 126A is amodulator. Following electronic or optical pumping of the gain medium122 by pump 124, a light pulse is released by active triggering of QSelement 126A.

In some embodiments, such as shown in FIG. 1C, illumination source 102Pis a P-QS laser including gain medium 122, pump 124, mirrors (not shown)and a SA 126P. SA 126P allows the laser cavity to store light energy(from pumping of gain medium 122 by pump 124) until a saturated level isreached in SA 126P, after which a “passive QS” light pulse is released.To detect the release of the passive QS pulse, a QS pulse photodetector128 is coupled to illumination source 102P. In some embodiments, QSpulse photodetector 128 is a Ge PD. The signal from QS pulsephotodetector 128 is used to trigger the receive process in receiver 110such that receiver 110 will be activated after a time period suitablefor target 104 distance to be imaged. The time period is derived asdescribed further below with reference to FIGS. 3B, 3C, 4B and 4C.

In some embodiments, the laser pulse duration from illumination source102 is in the range from 100 ps to 1 microsecond. In some embodiments,laser pulse energy is in the range from 10 microjoules to 100millijoule. In some embodiments, the laser pulse period is of the orderof 100 microseconds. In some embodiments, the laser pulse period is in arange from 1 microsecond to 100 milliseconds.

Gain medium 122 is provided in the form of a crystal or alternatively ina ceramic form. Non-limiting examples of materials that can be used forgain medium 122 include: Nd:YAG, Nd:YVO4, Nd:YLF, Nd:Glass, Nd:GdVO4,Nd:GGG, Nd:KGW, Nd:KYW, Nd:YALO, Nd:YAP, Nd:LSB, Nd:S-FAP, Nd:Cr:GSGG,Nd:Cr:YSGG, Nd:YSAG, Nd:Y2O3, Nd:Sc2O3, Er:Glass, Er:YAG, and so forth.In some embodiments, doping levels of the gain medium can be variedbased on the need for a specific gain. Non-limiting examples of SAs 126Pinclude: Co2+:MgAl2O4, Co2+:Spinel, Co2+:ZnSe and other cobalt-dopedcrystals, V3+:YAG, doped glasses, quantum dots, semiconductor SA mirror(SESAM), Cr4+YAG SA and so forth. Additional ways in which P-QS laser102P may be implemented are discussed below with respect to FIG. 6through 11, and any variations discussed with respect to a laser 600 maybe implemented also for illumination source 102P, mutatis mutandis.

Referring to illumination source 102, it is noted that pulsed laserswith sufficient power and sufficiently short pulses are more difficultto attain and more expensive than non-pulsed illumination, especiallywhen eye-safe SWIR radiation in solar absorption based is required.

Receiver 110 may include one or more Ge PDs 118 and receiver optics 116.In some embodiments, receiver 110 includes a 2D array of Ge PDs 118.Receiver 110 is selected to be sensitive to infrared radiation,including at least the wavelengths transmitted by illumination source102, such that the receiver may form imagery of the illuminated target104 from reflected radiation 108.

Receiver optics 116 may include one or more optical elements, such asmirrors or lenses that are arranged to collect, concentrate andoptionally filter the reflected electromagnetic radiation 228, and focusthe electromagnetic radiation onto a focal plane of receiver 110.

Receiver 110 produces electrical signals in response to electromagneticradiation detected by one or more of Ge PD 118 representative of imageryof the illuminated scene. Signals detected by receiver 110 can betransferred to internal image processor 114 or to an external imageprocessor (not shown) for processing into a SWIR image of the target104. In some embodiments, receiver 110 is activated multiple times tocreate “time slices” each covering a specific distance range. In someembodiments, image processor 114 combines these slices to create asingle image with greater visual depth such as proposed by Gruber,Tobias, et al. “Gated2depth: Real-time dense LIDAR from gated images.”arXiv preprint arXiv:1902.04997 (2019), which is incorporated herein byreference in its entirety.

In the automotive field, the image of target 104 within the field ofview (FOV) of receiver 110 generated by imaging systems 100′ or 100″ maybe processed to provide various driver assistance and safety features,such as: forward collision warning (FCW), lane departure warning (LDW),traffic sign recognition (TSR), and the detection of relevant entitiessuch as pedestrians or oncoming vehicles. The generated image may alsobe displayed to the driver, for example projected on a head-up display(HUD) on the vehicle windshield. Additionally or alternatively imagingsystems 100′ or 100″ may interface to a vehicle ECU 120 for providingimages or video to enable autonomous driving at low light levels or inpoor visibility conditions.

In active imaging scenarios, a light source, e.g. laser, is used incombination with an array of photoreceivers. Since the Ge PD operates inthe SWIR band, high power light pulses are feasible without exceedingeye safety regulations. For implementations in automotive scenarios, atypical pulse length is ˜100 ns, although, in some embodiments, longerpulse durations of up to about 1 microsecond are also anticipated.Considering eye safety, a peak pulse power of ˜300 KW is allowable, butthis level cannot practically be achieved by current laser diodes. Inthe present system the high-power pulses are therefore generated by a QSlaser. In some embodiments, the laser is a P-QS laser to further reducecosts. In some embodiments, the laser is actively QS.

As used herein the term “target” refers to any of an imaged entity,object, area, or scene. Non-limiting examples of targets in automotiveapplications include vehicles, pedestrians, physical barriers or otherobjects.

According to some embodiments, an active imaging system includes: anillumination source for emitting a radiation pulse towards a targetresulting in reflected radiation from the target, wherein theillumination source includes a QS laser; and a receiver including one ormore Ge PDs for receiving the reflected radiation. In some embodiments,the illumination source operates in the SWIR spectral band.

In some embodiments, the QS laser is an active QS laser. In someembodiments, the QS laser is a P-QS laser. In some embodiments, the P-QSlaser includes a SA. In some embodiments, the SA is selected from thegroup consisting of: Co2+:MgAl2O4, Co2+:Spinel, Co2+:ZnSe and othercobalt-doped crystals, V3+:YAG, doped glasses, quantum dots,semiconductor SA mirror (SESAM), and Cr4+YAG SA.

In some embodiments, the system further includes a QS pulsephotodetector for detecting of a radiation pulse emitted by the P-QSlaser. In some embodiments, the receiver is configured to be activatedat a time sufficient for the radiation pulse to travel to a target andreturn to the receiver. In some embodiments, the receiver is activatedfor an integration time during which the dark current power of the Ge PDdoes not exceed the kTC noise power of the Ge PD.

In some embodiments, the receiver produces electrical signals inresponse to the reflected radiation received by the Ge PDs, wherein theelectrical signals are representative of imagery of the targetilluminated by the radiation pulse. In some embodiments, the electricalsignals are processed by one of an internal image processor or anexternal image processor into an image of the target. In someembodiments, the image of the target is processed to provide one or moreof forward collision warning, lane departure warning, traffic signrecognition, and detection of pedestrians or oncoming vehicles.

According to further embodiments, a method for performing active imagingcomprises: releasing a light pulse by an illumination source comprisingan active QS laser; and after a time sufficient for the light pulse totravel to a target and return to the QS laser, activating a receivercomprising one or more Ge PDs for a limited time period for receiving areflected light pulse reflected from the target. In some embodiments,the illumination source operates in the shortwave infrared (SWIR)spectral band. In some embodiments, the limited time period isequivalent to an integration time during which a dark current power ofthe Ge PD does not exceed a kTC noise power of the Ge PD.

In some embodiments, the receiver produces electrical signals inresponse to the reflected light pulse received by the Ge PDs wherein theelectrical signals are representative of imagery of the targetilluminated by the light pulse. In some embodiments, the electricalsignals are processed by one of an internal image processor or anexternal image processor into an image of the target. In someembodiments, the image of the target is processed to provide one or moreof forward collision warning, lane departure warning, traffic signrecognition, and detection of pedestrians or oncoming vehicles.

According to further embodiments, a method for performing active imagingcomprises: pumping a P-QS laser comprising a SA to cause release of alight pulse when the SA is saturated; detecting the release of the lightpulse by a QS pulse photodetector; and after a time sufficient for thelight pulse to travel to a target and return to the QS laser based onthe detected light pulse release, activating a receiver comprising oneor more Ge PDs for a limited time period for receiving the reflectedlight pulse. In some embodiments, the QS laser operates in the shortwaveinfrared (SWIR) spectral band.

In some embodiments, the SA is selected from the group consisting ofCo2+:MgAl2O4, Co2+:Spinel, Co2+:ZnSe, other cobalt-doped crystals,V3+:YAG, doped glasses, quantum dots, semiconductor SA mirror (SESAM)and Cr4+YAG SA. In some embodiments, the limited time period isequivalent to an integration time during which the dark current power ofthe Ge PD does not exceed the kTC noise power of the Ge PD.

In some embodiments, the receiver produces electrical signals inresponse to the reflected light pulse received by the Ge PDs wherein theelectrical signals are representative of imagery of the targetilluminated by the light pulse. In some embodiments, the electricalsignals are processed by one of an internal image processor or anexternal image processor into an image of the target. In someembodiments, the image of the target is processed to provide one or moreof forward collision warning, lane departure warning, traffic signrecognition, and detection of pedestrians or oncoming vehicles.

Exemplary embodiments relate to a system and method for high SNR activeSWIR imaging using Ge based PDs. In some embodiments, the imaging systemis a gated imaging system. In some embodiments, the pulsed illuminationsource is an active or P-QS laser.

Reference is now made to FIGS. 3A, 3B and 3C that show, respectively, aflowchart and schematic drawings of a method of operation of an activeSWIR imaging system according to some embodiments. Process 300 shown inFIG. 3A is based on system 100′ as described with reference to FIG. 1B.In step 302, pump 124 of illumination source 102A is activated to pumpgain medium 122. In step 304, active QS element 126A releases a lightpulse in the direction of a target 104 that is at a distance of D. Instep 306, at Time=T, the light pulse strikes target 104 and generatesreflected radiation back towards system 100′ and receiver 110. In step308, after waiting a time=T2, receiver 110 is activated to receive thereflected radiation. The return propagation delay T2 consists of theflight time of the pulse from illumination source 102A to target 104plus the flight time of the optical signal reflected from target 104. T2is therefore known for a target 104 at a distance “D” from theillumination source 102A and receiver 110. The activation period ofreceiver 110 Δt is determined based on the required depth of view (DoV).The DoV is given by 2DoV=c*Δt where c is the speed of light. A typicalΔt of 100 ns provides a depth of view of 15 meters. In step 310, thereflected radiation is received by receiver 110 for a period of Δt. Thereceived data from receiver 110 is processed by image processor 114 (oran external image processor) to generate a received image. Process 300can be repeated N times in each frame, where a frame is defined as thedata set transferred from receiver 110 to image processor 114 (or to anexternal image processor). In some embodiments, N is between 1 and10,000.

Reference is now made to FIGS. 4A, 4B and 4C that show, respectively, aflowchart and schematic drawings of an exemplary method of operation ofan active SWIR imaging system according to some embodiments. A process400 shown in FIG. 4A is based on system 100″ as described with referenceto FIG. 1C. In step 402, pump 124 of illumination source 102P isactivated to pump gain medium 122 and to saturate SA 126P. In step 404,after reaching a saturation level, SA 126P releases a light pulse in thedirection of a target 430 at a distance of D. In step 406, QS pulsephotodetector 128 detects the released light pulse. In step 408, atTime=T, the light pulse strikes target 430 and generates reflectedradiation back towards system 100″ and receiver 110. In step 410, afterwaiting a time=T2 following the detection of a released light pulse byQS pulse photodetector 128, receiver 110 is activated to receive thereflected radiation. The return propagation delay T2 comprises theflight time of the pulse from illumination source 102P to target 430plus the flight time of the optical signal reflected from target 430. T2is therefore known for a target 430 at a distance “D” from theillumination source 102P and receiver 110. The activation period of Δtis determined based on the required depth of view (DoV). In step 412,the reflected radiation is received by receiver 110 for a period of Δt.The received data from receiver 110 is processed by image processor 114(or by an external image processor) to generate a received image.Process 400 can be repeated N times in each frame. In some embodiments,N is between 1 and 10,000.

Referring to all of imaging systems 100, 100′ and 100″, it is noted thatany one of those imaging systems may include readout circuitry forreading out, after the integration time, an accumulation of chargecollected by each of the Ge PDs, to provide the detection signal for therespective PD. That it, unlike LIDARs or other depth sensors, thereading out process may be executed after the concussion of theintegration time and therefore after the signal from a wide range ofdistances as irreversibly summed.

Referring to all of imaging systems 100, 100′ and 100″, optionallyreceiver 110 outputs a set of detection signals representative of thecharge accumulated by each of the plurality of Ge PDs over theintegration time, wherein the set of detection signals is representativeof imagery of the target as illuminated by at least one SWIR radiationpulse.

Referring to all of imaging systems 100, 100′ and 100″, the imagingsystem may optionally at least one diffractive optics element (DOE)operative to improve illumination uniformity of light of the pulsedillumination source before the emission of light towards the target. Asaforementioned, a high peak power pulsed light source 102 may issue aninsufficiently uniform illumination distribution over different parts ofthe FOV. The DOE (not illustrated) may improve uniformity of theillumination to generate high quality images of the FOV. It is notedthat equivalent illumination uniformity is usually not required in LIDARsystems and other depth sensors, which may therefore not include DOEelements for reasons of cost, system complexity, system volume, and soon. In LIDAR systems, for example, as long as the entire FOV receivesufficient illumination (above a threshold which allows detection oftarget at a minimal required distance), it does not matter if some areasin the FOV receive substantially more illumination density than otherparts of the FOV. The DOE of system 100, if implemented, may be used forexample for reducing speckle effects. It is noted that imaging systems100, 100′ and 100″ may also include other types of optics for directinglight from light source 102 to the FOV, such as lenses, mirrors, prisms,waveguides, etc.

Referring to all of imaging systems 100, 100′ and 100″, controller 112may optionally be operative to activate receiver 110 to sequentiallyacquire a series of gated images, each representative of the detectionsignals of the different Ge PDs at a different distance range, and animage processor operative to combine the series of image into a singletwo dimensional image. For example, a first image may acquire lightbetween 0-50 m, a second image may acquire light between 50-100 m and athird image may acquire light between 100-125 m from the imaging sensor,and image processor 114 may combine the plurality of 2D images to asingle 2D images. This way, each distance range is captured withaccumulated dark current noise that is still lesser than the readoutnoise introduced by the readout circuitry, in the expense of using morelight pulses and more computation. The color value for each pixel of thefinal image (e.g., grayscale value) may be determined as a function ofthe respective pixels in the gated images (e.g., a maximum of allvalues, or a weighted average).

Referring to all of imaging systems 100, 100′ and 100″, the imagingsystem may be an uncooled Ge-based SWIR imaging system, operative todetect a 1 m×1 m target with a SWIR reflectivity (at the relevantspectral range) of 20% at a distance of more than 50 m.

Referring to all of imaging systems 100, 100′ and 100″, pulsedillumination source 102 may be a QS laser operative to emit eye safelaser pulses having pulse energy between 10 millijoule and 100millijoule. While not necessarily so, the illumination wavelength may beselected to match a solar absorption band (e.g., the illuminationwavelength may be between 1.3 μm and 1.4 μm.

Referring to all of imaging systems 100, 100′ and 100″, the outputsignal by each Ge PD used for image generation may be representative ofa single scalar for each PD. Referring to all of imaging systems 100,100′ and 100″, each PD may output an accumulated signal that isrepresentative of a wide range of distances. For example, some, most, orall of the Ge PDs of receiver 110 may output detection signals which arerepresentative each of light reflected to the respective PD from 20 m,from 40 m and from 60 m.

Further distinguishing feature of imaging systems 100, 100′ and 100″over many known art systems is that the pulsed illumination is not usedto freeze fast motion of objects in the field (unlike photography flashillumination, for example) and is used the same for static scenes. Yetanother distinguishing feature of imaging systems 100, 100′ and 100″over many known art systems is that the gating of the image is not usedprimarily to avoid internal noise in the system, in comparison toexternal noise, which is a nuisance for some known art (e.g., sunlight).

It is noted that any one of the components, features, modes ofoperation, system architectures and internal relationships discussedabove with respect to systems 100, 100′ and 100″ may be implemented,mutatis mutandis, in any of the EO systems discussed below, such assystems 700, 1300, 1300′, 1600, 1600′, 1700, 1800, 1900, 2300 and 3600.

FIG. 5 is a flowchart illustrating a method 500 for generating SWIRimages of objects in a FOV of an EO system, in accordance with examplesof the presently disclosed subject matter. Referring to the examples setforth with respect to the previous drawings, method 500 may be executedby any one of imaging systems 100, 100′ and 100″. It is noted thatmethod 500 may also be implemented by any active imaging systemdescribed below (such as systems 700, 1300, 1300′, 1600, 1600′, 1700,1800, 1900, 2300 and 3600).

Method 500 starts with a step (or “stage”) 510 of emitting at least oneillumination pulse toward the FOV, resulting in SWIR radiationreflecting from at least one target. Hereinafter, “step” and “stage” areused interchangeably. Optionally, the one or more pulses may be highpeak power pulse. Utilization of multiple illumination pulses may berequired, for example, to achieve an overall higher level ofillumination when compared to a single pulse. Referring to the examplesof the accompanying drawings, step 510 may optionally be carried out bycontroller 112.

A step 520 includes triggering initiation of continuous signalacquisition by an imaging receiver that includes a plurality of Ge PDs(in the sense discussed above with respect to receiver 110) which isoperative to detect the reflected SWIR radiation. The continuous signalacquisition of step 520 means that the charge is collected continuouslyand irreversibly (i.e., it is impossible to learn what level of chargewas collected in any intermediate time), and not in small increments.The triggering of step 520 may be executed before step 510 (for example,if the detection array requires a ramp up time), concurrently with step510, or after step 510 concluded (e.g., to start detecting at a nonzerodistance from the system). Referring to the examples of the accompanyingdrawings, step 520 may optionally be carried out by controller 112.

A step 530 starts after the triggering of step 520 and includescollecting for each of the plurality of Ge PDs, as a result of thetriggering, charge resulting from at least the impinging of the SWIRreflection radiation on the respective Ge PD, dark current that islarger than 50 μA/cm², integration-time dependent dark current noise,and integration-time independent readout noise. Referring to theexamples of the accompanying drawings, step 530 may optionally becarried out by receiver 110.

A step 540 includes triggering ceasing of the collection of the chargewhen the amount of charge collected as a result of dark current noise isstill lower than the amount of charge collected as a result of theintegration-time independent readout noise. The integration time is theduration of step 530 until the ceasing of step 540. Referring to theexamples of the accompanying drawings, step 540 may optionally becarried out by controller 112.

A step 560 is executed after step 540 is concluded, and it includesgenerating an image of the FOV based on the levels of charge collectedby each of the plurality of Ge PDs. As aforementioned with respect toimaging systems 100, 100′ and 100″, the image generated in step 560 is a2D image with no depth information. Referring to the examples of theaccompanying drawings, step 560 may optionally be carried out by imagingprocessor 114.

Optionally, the ceasing of the collection as a result of step 540 may befollowed by optional step 550 reading by readout circuitry a signalcorrelated to the amount of charge collected by each of the Ge PDs,amplifying the read signal, and providing the amplified signals(optionally after further processing) to an image processor that carriesout the generation of the image as step 560. Referring to the examplesof the accompanying drawings, step 550 may optionally be carried out bythe readout circuitry (not illustrated above, but may be equivalent toany of the readout circuitries discussed below, such as readoutcircuitry 1610, 2318 and 3630). It is noted that step 550 is optionalbecause other suitable methods of reading out the detection results fromthe Ge PSs may be implemented.

Optionally, the signal output by each out of multiple Ge PDs is a scalarindicative of amount of light reflected from 20 m, light reflected from40 m and light reflected from 60 m.

Optionally, the generating of step 560 may include generating the imagebased on a scalar value read for each of the plurality of Ge PDs.Optionally, the emitting of step 510 may include increasing illuminationuniformity of pulsed laser illumination by passing the pulsed laserillumination (by one or more lasers) through at least one diffractiveoptics element (DOE), and emitting the detracted light to the FOV.Optionally, the dark current is greater than 50 picoampere per Ge PD.Optionally, the Ge PDs are Si—Ge PDs, each including both Silicon andGe. Optionally, the emitting is carried out by at least one active QSlaser. Optionally, the emitting is carried out by at least one P-QSlaser. Optionally, the collecting is executed when the receiver isoperating at a temperature higher than 30° C., and processing the imageof the FOV to detect a plurality of vehicles and a plurality ofpedestrians at a plurality of ranges between 50 m and 150 m. optionally,the emitting includes emitting a plurality of the illumination pulseshaving pulse energy between 10 millijoule and 100 millijoule into anunprotected eye of a person at a distance of less than 1 m withoutdamaging the eye.

As aforementioned with respect to active imaging systems 100, 100′ and100″, several gated images may be combined to a single image.Optionally, method 500 may include repeating multiple times the sequenceof emitting, triggering, collecting and ceasing; triggering theacquisition at a different time from the emitting of light at everysequence. At each sequence method 500 may include reading from thereceiver a detection value for each of the Ge PDs corresponding to adifferent distance range that is wider than 2 m (e.g., 2.1 m, 5 m, 10 m,25 m, 50 m, 100 m). The generating of the image in step 560 in such acase includes generating a single two-dimensional image based on thedetection values read from the different Ge PDs at the differentsequences. It is noted that since only several images are taken, thegated images are not sparse (i.e. in all or most of them, there aredetection values for many of the pixels). It is also noted that thegated images may have overlapping distance ranges. For example, a firstimage may represent the distances range 0-60 m, a second image mayrepresent the distances range 50-100 m, and a third image may representthe distances range 90-120 m.

FIGS. 6 through 11C demonstrate SWIR electro-optical (EO) systems andP-QS lasers which may be used in such systems, as well as methods foroperation and manufacturing of such lasers.

FIG. 10 is a schematic functional block diagram illustrating an exampleof SWIR optical system 700, in accordance with examples of the presentlydisclosed subject matter. System 700 comprises at least P-QS laser 600,but may also comprise, as shown in FIG. 10, additional components suchas:

a. a sensor 702 operative to sense reflected light from the FOV ofsystem 700, and especially reflected illumination of laser 600 reflectedfrom external objects 910. Referring to the other examples, sensor 702may be implemented as imaging receiver, PDA or photodetecting devicesdiscussed in the present disclosure, such as components 110, 1300,1300′, 1600, 1600′, 1700, 1800, 1900, 2302 and 3610.b. a processor 710, operative to process the sensing results of sensor702. The output of the processing may be an image of the FOV, a depthmodel of the FOV, spectroscopy analysis of one or more parts of the FOV,information of identified objects in the FOV, light statistics on theFOV, or any other type of output. Referring to the other examples,processor 710 may be implemented as any one of the processors discussedin the present disclosure, such as processors 114, 1908, 2304 and 3620.c. a controller 712, operative to control activity of laser 600 and/orprocessor 710. For example, controller 712 may include controllingtiming, synching, and other operational parameters of processor 710and/or laser 600. Referring to the other examples, controller 712 may beimplemented as any one of the other controllers discussed in the presentdisclosure, such as controller 112, 1338, 2314 and 3640.

Optionally, system 700 may include a SWIR PDA 706 sensitive to thewavelength of the laser. This way SWIR optical system may serve as anactive SWIR camera, SWIR time-of-flight (ToF) sensor, SWIR lightdetection and ranging (LIDAR) sensor, and so on. The ToF sensor may besensitive to the wavelength of the laser. Optionally, the PDA may be aCMOS based PDA which is sensitive to SWIR frequencies emitted by laser600, such is a CMOS based PDAs designed and manufactured by TriEye LTD.of Tel Aviv, Israel.

Optionally, system 700 may include a processor 710 for processingdetection data from the SWIR PDA (or any other light sensitive sensor ofsystem 700). For example, the processor may process the detectioninformation to provide a SWIR image of a field-of-view (FOV) of system700, to detect objects in the FOV, and so on. Optionally, the SWIRoptical system may include a time of flight (ToF) SWIR sensor sensitiveto the wavelength of the laser, and a controller operative tosynchronize operation of the ToF SWIR sensor and the P-QS SWIR laser fordetecting a distance to at least one object in the field of view of theSWIR optical system. Optionally, system 700 may include controller 712operative to control one or more aspects of an operation of laser 600 orother components of the system such as the photodetector array (e.g.,focal plane array, FPA). For example, some of the parameters of thelaser which may be controlled by the controller include timing,duration, intensity, focusing, and so on. While not necessarily so, thecontroller may control operation of the laser based on detection resultsof the PDA (directly, or based on processing by the processor).Optionally, the controller may be operative to control the laser pump orother type of light source to affect activation parameters of the laser.Optionally, the controller may be operative to dynamically change thepulse repetition rate. Optionally, the controller may be operative tocontrol dynamic modification of the light shaping optics, e.g., forimproving a Signal to Noise Ratio (SNR) in specific regions of the fieldof view. Optionally, the controller may be operative to control theillumination module for dynamically changing pulse energy and/orduration, (e.g., in the same ways possible for other P-QS lasers, suchas changing focusing of pumping laser, etc.)

Further and optionally, system 700 may include temperature control(e.g., passive temperature control, active temperature control) forcontrolling a temperature of the laser generally, or of one or more ofits components (e.g., of the pump diode). Such temperature control mayinclude, for example, a thermoelectric cooler (TEC), a fan, a heat sink,resistance heater under pump diode, and so forth.

Further and optionally, system 700 may include another laser which usedto bleach at least one of GM 602 and SA 604. Optionally, system 700 mayinclude an internal photosensitive detector (e.g., one or more PDs likePDA 706) which is operative to measure a time in which a pulse isgenerated by laser 600 (e.g., as PD 226 as discussed above). In suchcase, controller 740 may be operative to issue, based on the timinginformation obtained from internal photosensitive detector 706, atriggering signal to PDA 706 (or other type of camera or sensor 702)which detects reflection of laser light from objects in the field ofview of system 700.

The main industry that has required high volumes of lasers in theaforementioned spectral range (1.3-1.5 μm) is the electronics industryfor optical data storage, which drove the diode laser cost down todollars, or less, per device, per Watt. However, those lasers are notsuitable for other industries such as the automotive industry, whichrequires lasers with considerably greater peak power and beambrightness, and which will be utilized in harsh environmentalconditions.

It is noted that there is no scientific consensus about the range ofwavelengths which are considered part of the SWIR spectrum.Nevertheless, for the purposes of the present disclosure, the SWIRspectrum includes electromagnetic radiation in wavelengths which arelonger than that of the visible spectrum, and which include at the veryleast the spectral range between 1,300 and 1,500 nm.

While not restricted to such uses, one or more P-QS lasers 600 may beused as illumination source 102 of any one of imaging systems 100, 100′and 100″. Laser 600 may be used in any other EO system operating in theSWIR range which requires pulsed illumination such as lidars,spectrographs, communication systems, and so on. It is noted that theproposed lasers 600 and methods for manufacturing of such lasers allowsfor high volume manufacturing of lasers operating in the SWIR spectralrange in relatively low production costs.

P-QS laser 600 includes at least a crystalline gain medium 602(hereinbelow gain medium is also referred to as “GM”), a crystalline SA604, and an optical cavity 606 in which the aforementioned crystallinematerials are confined, to allow light propagating within gain medium602 to intensify towards producing a laser light beam 612 (illustratedfor example in FIG. 8). The optical cavity is also known by the terms“optical resonator” and “resonating cavity”, and it includes a highreflectivity mirror 608 (also referred to as “high reflector”) and anoutput coupler 610. Discussed below are several unique and novelcombinations of crystalline materials of different types, and usingvaried manufacturing techniques for manufacturing the lasers, whichallow for high volume manufacturing of reasonably priced lasers for theSWIR spectral range. General details which are generally known in theart with respect to P-QS lasers are not provided here for reasons ofconciseness of the disclosure, but are readily available from a widevariety of resources. The saturable absorber of the laser serves as theQ-switch for the laser, as is known in the art. The term “crystallinematerial” broadly includes any material which is in eithermonocrystalline form or polycrystalline form.

The dimensions of the connected crystalline gain medium and crystallineSA may depend on the purpose for which a specific P-QS laser 600 isdesigned. In a non-limiting example, a combined length of the SA and theGM is between 5 and 15 millimeters. In a non-limiting example, thecombined length of the SA and the GM is between 2 and 40 millimeters. Ina non-limiting example, a diameter of the combination of SA and GM(e.g., if a round cylinder, or confined within an imaginary suchcylinder) is between 2 and 5 millimeters. In a non-limiting example, adiameter of the combination of SA and GM is between 0.5 and 10millimeters.

P-QS laser 600 includes a gain medium crystalline material (GMC) whichis rigidly connected to a SA crystalline material (SAC). The rigidcoupling may be implemented in any one of the ways known in the art suchas using adhesive, diffusion bonding, composite crystal bonding, growingone on top of the other, and so on. However, as discussed below, rigidlyconnecting crystalline materials which are in a ceramic form may beachieved using simple and cheap means. It is noted that the GMC and theSAC material may be rigidly connected directly to one another, but mayoptionally be rigidly connected to one another via an intermediateobject (e.g., another crystal). In some implementation, both the gainmedium and the SA may be implemented on single piece of crystallinematerial, by doping different parts of the single piece of crystallinematerial with different dopants (such as the ones discussed below withrespect to SAC materials and to GMC materials), or by co-doping a singlepiece of crystalline material, doping the same volume of the crystallinematerial with the two dopants (e.g., a ceramic YAG co-doped with N³⁺ andV³⁺). Optionally, the gain medium may be grown on a single crystalsaturable absorbing substrate (e.g., using Liquid Phase Epitaxy, LPE).It is noted that separate GMC materials and SA crystalline materials arediscussed extensively in the disclosure below, a single piece of ceramiccrystalline material doped with two dopants may also be used in any ofthe following implementations, mutatis mutandis.

FIGS. 7A, 7B and 7C are schematic functional block diagrams illustratingexamples of P-QS laser 600, in accordance with the presently disclosedsubject matter. In FIG. 7A the two dopants are implemented on two partsof the common crystalline material 614 (acting both as GM and as SA),while in FIG. 7B the two dopants are implemented interchangeably oncommon volume of the common crystalline material 614 (in the illustratedcase—the entirety of the common crystal). Optionally, the GM and the SAmay be implemented on a single piece of crystalline material doped withneodymium and at least one other material. Optionally (e.g., asexemplified in FIG. 7C), any one or both of output coupler 610 and highreflectivity mirror 608 may be glued directly to one of the crystallinematerials (e.g., the GM or the SA, or a crystal combining both).

At least one of SAC and the GMC is a ceramic crystalline material, whichis the relevant crystalline material (e.g., doped yttrium aluminumgarnet, YAG, doped vanadium) in a ceramic form (e.g., a polycrystallineform). Having one—and especially both—crystalline material in ceramicform allows for production in higher numbers and in lower costs. Forexample, instead of growing separate monocrystalline materials in a slowand limited process, polycrystalline materials may be manufactured bysintering of powders (i.e., compacting and possibly heating a powder toform a solid mass), low temperature sintering, vacuum sintering, and soon. One of the crystalline materials (SAC or GMC) may be sintered on topof the other, obviating the need for complex and costly processes suchas polishing, diffusion bonding, or surface activated bonding.Optionally, at least one of the GMC and SAC is polycrystalline.Optionally, both the GMC and the SAC is polycrystalline.

Referring to the combinations of crystalline materials from which theGMC and the SAC may be made, such combinations may include:

a. The GMC is ceramic neodymium-doped yttrium aluminum garnet (Nd:YAG)and the SAC is either (a) ceramic three-valence vanadium-doped yttriumaluminum garnet (V³⁺:YAG), or (b) a ceramic Cobalt-doped crystallinematerial. Optionally, the ceramic Cobalt-doped crystalline material maybe two-valence ceramic Cobalt-doped crystalline material. In thosealternatives, both the Nd:YAG and the SAC selected from theaforementioned group are in ceramic form. A cobalt-doped crystallinematerial is a crystalline material which is doped with cobalt. Examplesinclude Cobalt-doped Spinel (Co:Spinel, or Co²⁺:MgAl₂O₄) cobalt-dopedZinc selenide (Co²⁺:ZnSe), cobalt-doped YAG (Co²⁺:YAG). While notnecessarily so, the high reflectivity mirror and the SA in this optionmay optionally be rigidly connected to the gain medium and the SA, suchthat the P-QS laser is a monolithic microchip P-QS laser (e.g., asexemplified in FIGS. 8 and 10).b. The GMC is a ceramic neodymium-doped yttrium aluminum garnet(Nd:YAG), and the SAC is a non-ceramic SAC selected from a group ofdoped ceramic materials consisting of: (a) three-valence vanadium-dopedyttrium aluminum garnet (V³⁺:YAG) and (b) Cobalt-doped crystallinematerials. Optionally, the Cobalt-doped crystalline material may betwo-valence Cobalt-doped crystalline material. In such case, highreflectivity mirror 608 and output coupler 610 are rigidly connected tothe gain medium and the SA, such that P-QS laser 600 is a monolithicmicrochip P-QS laser.c. The GMC which is ceramic neodymium-doped rare-earth elementcrystalline material, and the SAC is a ceramic crystalline materialselected from a group of doped crystalline materials consisting of: (a)three-valence vanadium-doped yttrium aluminum garnet (V³⁺:YAG) and (b)Cobalt-doped crystalline materials. Optionally, the Cobalt-dopedcrystalline material may be two-valence Cobalt-doped crystallinematerial. While not necessarily so, high reflectivity mirror 608 andoutput coupler 610 in this option may optionally be rigidly connected tothe gain medium and the SA, such that P-QS laser 600 is a monolithicmicrochip P-QS laser.

It is noted that in any one of the implementations, a doped crystallinematerial may be doped with more than one dopant. For example, the SACmay be doped with the main dopant disclosed above, and with at least oneother doping material (e.g., in significantly lower quantities). Aneodymium-doped rare-earth element crystalline material is a crystallinematerial whose unit cell comprises a rare-earth element (one of awell-defined group of 15 chemical elements, including the fifteenlanthanide elements, as well as scandium and yttrium) and which is dopedwith neodymium (e.g., triply ionized neodymium) which replaces therear-earth element in a fraction of the unit cells. Few non-limitingexamples of neodymium-doped rare-earth element crystalline materialwhich may be used in the disclosure are:

a. Nd:YAG (as mentioned above), neodymium-doped tungstic acid yttriumpotassium (Nd:KYW), neodymium-doped yttrium lithium fluoride (Nd:YLF),neodymium-doped yttrium orthovanadate (YVO₄), in all of which therear-earth element is Neodymium, Nd;b. Neodymium-doped gadolinium orthovanadate (Nd:GdVO₄), neodymium-dopedGadolinium Gallium Garnet (Nd:GGG), neodymium-doped potassium-gadoliniumtungstate (Nd:KGW), in all of which the rear-earth element isgadolinium, Gd);c. Neodymium-doped lanthanum scandium borate (Nd:LSB) in which therare-earth element is scandium);d. Other neodymium-doped rare-earth element crystalline materials may beused, in which the rare-earth element may be yttrium, gadolinium,scandium, or any other rare-earth element.

The following discussion applies to any of the optional combinations ofGMCs and SACs.

Optionally, the GMC is rigidly connected directly to the SAC.Alternatively, the GMC and the SAC may be connected indirectly (e.g.,each of the SAC and GMC being connected via a group of one or moreintermediate crystalline materials and/or via one or more other solidmaterials transparent to the relevant wavelengths). Optionally one orboth of the SAC and the GMC are transparent to the relevant wavelengths.

Optionally, the SAC may be cobalt-doped Spinel (Co Co²⁺:MgAl₂O₄).Optionally, the SAC may be cobalt-doped YAG (Co:YAG). Optionally, thismay enable co-doping of cobalt and neodymium Nd on the same YAG.Optionally, the SAC may be cobalt-doped Zinc selenide (Co²⁺:ZnSe).Optionally, the GMC may be a ceramic cobalt-doped crystalline material.

Optionally, an initial transmission (To) of the SA is between 75% and90%. Optionally, the initial transmission of the SA is between 78% and82%.

The wavelengths emitted by the laser depend on the material used in itsconstruction, and especially on the materials and dopants of the GMC andthe SAC. Some examples of output wavelengths include wavelengths in therange of 1,300 nm and 1,500 nm. Some more specific examples include 1.32μm or about 1.32 μm (e.g., 1.32 μm±3 nm), 1.34 μm or about 1.34 μm(e.g., 1.34 μm±3 nm), 1.44 μm or about 1.44 μm (e.g., 1.44 μm±3 nm). Acorresponding imager sensitive to one or more of these light frequencyranges may be included in SWIR optical system 700 (e.g., as exemplifiedin FIG. 10).

FIGS. 8 and 9 are schematic functional diagrams illustrating SWIRoptical system 700, in accordance with examples of the presentlydisclosed subject matter. As exemplified in these illustrations, laser600 may include additional components in addition to those discussedabove, such as (but not limited to):

a. A light source such as a flashlamp 616 or a laser diode 618 whichserves as a pump for the laser. Referring to the previous examples, thelight source may serve as pump 124.b. Focusing optics 620 (e.g., lenses) for focusing light from the lightsource (e.g. 618) onto the optical axis of laser 600.c. A diffuser or other optics 622 for manipulating laser beam 612 afterit exits optical cavity 606.

Optionally, SWIR optical system 700 may include optics 708 to spread thelaser over a wider FOV, to improve eye safety issues in the FOV.Optionally, SWIR optical system 700 may include optics 704 to collectreflected laser light from the FOV and directing it onto the sensor 702,e.g., onto a photodetector array (PDA) 706, see FIG. 10. Optionally theP-QS laser 600 is a diode pumped solid state laser (DPSSL).

Optionally, P-QS laser 600 includes at least one diode pump light source872 and optics 620 for focusing light of the diode pump light sourceinto the optical resonator (optical cavity). Optionally, the lightsource is positioned on the optical axis (as an end pump). Optionally,the light source may be rigidly connected to high reflectivity mirror608 or to SA 604, such that the light source is a part of a monolithicmicrochip P-QS laser. Optionally, the light source of the laser mayinclude one or more vertical-cavity surface-emitting laser (VCSEL)array. Optionally, P-QS laser 600 includes at least one VCSEL array andoptics for focusing light of the VCSEL array into the optical resonator.The wavelengths emitted by the light source (e.g., the laser pump) maydepend on the crystalline materials and/or dopants used in the laser.Some example pumping wavelengths which may be emitted by the pumpinclude: 808 nm or about 808 nm, 869 nm or about 869 nm, about ninehundred and some nm.

The power of the laser may depend on the utilization for which it isdesigned. For example, the laser output power may be between 1 W and 5W. For example, the laser output power may be between 5 W and 15 W. Forexample, the laser output power may be between 15 W and 50 W. Forexample, the laser output power may be between 50 W and 200 W. Forexample, the laser output power may be higher than 200 W.

QS laser 600 is a pulsed laser, and may have different frequency(repetition rate), different pulse energy, and different pulse duration,which may depend on the utilization for which it is designed. Forexample, a repetition rate of the laser may be between 10 Hz and 50 Hz.For example, a repetition rate of the laser may be between 50 Hz and 150Hz. For example, a pulse energy of the laser may be between 0.1 mJ and 1mJ. For example, a pulse energy of the laser may be between 1 mJ and 2mJ. For example, a pulse energy of the laser may be between 2 mJ and 5mJ. For example, a pulse energy of the laser may be higher than 5 mJ.For example, a pulse duration of the laser may be between 10 ns and 100ns. For example, a pulse duration of the laser may be between 0.1 μs and100 μs. For example, a pulse duration of the laser may be between 100 μsand 1 ms. The size of the laser may also change, depending for exampleon the size of its components. For example, the laser dimensions may beX₁ by X₂ by X₃, wherein each of the dimensions (X₁, X₂, and X₃) isbetween 10 mm and 100 mm, between 20 and 200 mm, and so on. The outputcoupling mirror may be flat, curved, or slightly curved.

Optionally, laser 600 may further include undoped YAG in addition to thegain medium and to the SA, for preventing heat from accumulating in anabsorptive region of the gain medium. The undoped YAG may optionally beshaped as a cylinder (e.g., a concentric cylinder) encircling the gainmedium and the SA.

FIG. 11A is a flow chart illustrating an example of method 1100, inaccordance with the presently disclosed subject matter. Method 1100 is amethod for manufacturing parts for a P-QS laser such as but not limitedto P-QS laser 600 discussed above. Referring to the examples set forthwith respect to the previous drawings, the P-QS laser may be laser 600.It is noted that any variation discussed with respect to laser 600 or toa component thereof may also be implemented for the P-QS laser whoseparts are manufactured in method 1100 or to a corresponding componentthereof, and vice versa.

Method 1100 starts with step 1102 of inserting into a first mold atleast one first powder, which is processed later in method 1100 to yielda first crystalline material. The first crystalline material serves aseither the GM or the SA of the P-QS laser. In some implementations thegain medium of the laser is made first (e.g., by way of sintering), andthe SA is made later on top of the previously made GM (e.g., by way ofsintering). On other implementations, the SA of the laser is made first,and the GM is made later on top of the previously made SA. In yet otherimplementations, the SA and the GM are made independently of oneanother, and are coupled to form a single rigid body. The coupling maybe done as part of the heating, sintering, or later.

Step 1104 of method 1100 includes inserting into a second mold at leastone second powder different than the at least one first powder. The atleast one second powder is processed later in method 1100 to yield asecond crystalline material. The second crystalline material serves aseither the GM or the SA of the P-QS laser (so that one of the SA and theGM is made from the first crystalline material and the otherfunctionality is made from the second crystalline material).

The second mold may be different from the first mold. Alternatively, thesecond mold may be the same as the first mold. In such case the at leastone second powder may be inserted, for example, on top of the at leastone first powder (or on top of the first green body, if already made),beside it, around it, and so on. The inserting of the at least onesecond powder into the same mold of the at least one first powder (ifimplemented) may be executed before processing of the at least one firstpowder into a first green body, after processing of the at least onefirst powder into the first green body, or sometime during theprocessing of the at least one first powder into the first green body.

The first powder and/or the second powder may include crushed YAG (orany of the other aforementioned materials such as Spinel, MgAl₂O₄, ZnSe)and doping materials (e.g., N³⁺, V³⁺, Co). The first powder and/or thesecond powder may include materials from which YAG (or any of the otheraforementioned materials such as Spinel, MgAl₂O₄, ZnSe) is made anddoping material (e.g., N³⁺, V³⁺, Co).

Step 1106 is executed after step 1102, and includes compacting the atleast one first powder in the first mold to yield a first green body.Step 1104 is executed after step 1108, that includes compacting the atleast one second powder in the second mold, thereby yielding a secondgreen body. If the at least one first powder and the at least one secondpowder are inserted into the same mold in steps 1102 and 1104, thecompacting of the powders in step 1106 and 1108 may be done concurrently(e.g., pressing on the at least one second powder, which in turncompresses the at least one first powder against the mold), but this isnot necessarily so. For example, step 1104 (and therefore also step1108) may optionally be executed after the compressing of step 1106.

Step 1110 includes heating the first green body to yield a firstcrystalline material. Step 1112 includes heating the second green bodyto yield a second crystalline material. In different embodiments, theheating of the first crystalline may be executed before, concurrently,partly concurrently, or after each one of steps 1106 and 1110.

Optionally, the heating of the first green body at step 1110 precedesthe compacting (and possibly also precedes the inserting) of the atleast one second powder in step 1108 (and possibly step 1104). The firstgreen body and the second green body may be heated separately (e.g., indifferent times, in different temperatures, for different durations).The first green body and the second green body may be heated together(e.g., in the same oven), either connected to each other during theheating or not. The first green body and the second green body may besubject to different heating regimes, which may share partialco-heating, while being heated separately in other parts of the heatingregimes. For example, one or both of the first green body and the secondgreen body may be heated separately from the other green body, and thenthe two green bodies may be heated together (e.g., after coupling, butnot necessarily so). Optionally, the heating of first green body and theheating of the second green body comprise concurrent heating of thefirst green body and the second green body in a single oven. It is notedthat optionally, the coupling of step 1114 is a result of the concurrentheating of both of the green bodies in the single oven. It is noted thatoptionally, the coupling of step 1114 is done by co-sintering both ofthe green bodies after being physically connected to one another.

Step 1116 includes coupling the second crystalline material to the firstcrystalline material. The coupling may be executed in any way ofcoupling known in the art, several non-limiting examples of which werediscussed above with respect to P-QS laser 600. It is noted that thecoupling may have several sub-steps, some of which may intertwine withdifferent steps out of steps 1106, 1108, 1110, and 1112 in differentmanners in different embodiments. The coupling results in a single rigidcrystalline body that includes both the GM and the SA.

It is noted that method 1100 may include additional steps which are usedin the making of crystals (and especially in the making of ceramic ornon-ceramic polycrystalline crystal compounds of polycrystallinematerials which are bounded to each other). Few non-limiting examplesinclude powder preparation, binder burn-out, densification, annealing,polishing (if required, as discussed below), and so on.

The GM of the P-QS laser in method 1100 (which, as aforementioned, canbe either the first crystalline material or the second crystallinematerial), is a neodymium-doped crystalline material. The SA of the P-QSlaser in method 1100 (which, as aforementioned, can be either the firstcrystalline material or the second crystalline material), is selectedfrom a group of crystalline materials consisting of: (a) aneodymium-doped crystalline material, and (b) a doped crystallinematerial selected from a group of doped crystalline materials consistingof: three-valence vanadium-doped yttrium aluminum garnet (V³⁺:YAG) andcobalt-doped crystalline materials. At least one of the GM and the SA isa ceramic crystalline material. Optionally, both of the GM and the SAare ceramic crystalline materials. Optionally, at least one of the GMand the SA is a polycrystalline material. Optionally, both the GM andthe SA are polycrystalline materials.

While additional steps of the manufacturing process may take placebetween the different stages of method 1100, notably polishing of thefirst material before bonding of the second material in the process ofsintering is not required in at least some of the implementations.

Referring to the combinations of crystalline materials from which theGMC and the SAC may be made in method 1100, such combinations mayinclude:

a. The GMC is ceramic neodymium-doped yttrium aluminum garnet (Nd:YAG),and the SAC is either (a) ceramic three-valence vanadium-doped yttriumaluminum garnet (V³⁺:YAG), or (b) a ceramic Cobalt-doped crystallinematerial. In this alternatives, both the Nd:YAG and the SAC selectedfrom the aforementioned group are in ceramic form. A cobalt-dopedcrystalline material is a crystalline material which is doped withcobalt. Examples include Cobalt-doped Spinel (Co:Spinel, orCo²⁺:MgAl₂O₄) cobalt-doped Zinc selenide (Co²⁺:ZnSe). While notnecessarily so, the high reflectivity mirror and the output coupler inthis option may optionally be rigidly connected to the GM and the SA,such that the P-QS laser is a monolithic microchip P-QS laser.b. The GMC is a ceramic neodymium-doped yttrium aluminum garnet(Nd:YAG), and the SAC is a nonceramic SAC selected from a group of dopedceramic materials consisting of: (a) three-valence vanadium-dopedyttrium aluminum garnet (V³⁺:YAG) and (b) Cobalt-doped crystallinematerials. In such case, the high reflectivity mirror and the outputcoupler are rigidly connected to the GM and the SA, such that the P-QSlaser is a monolithic microchip P-QS laser.c. The GMC which is ceramic neodymium-doped rare-earth elementcrystalline material, and the SAC is a ceramic crystalline materialselected from a group of doped crystalline materials consisting of: (a)three-valence vanadium-doped yttrium aluminum garnet (V³⁺:YAG) and (b)Cobalt-doped crystalline materials. While not necessarily so, the highreflectivity mirror and the output coupler in this option may optionallybe rigidly connected to the GM and the SA, such that the P-QS laser is amonolithic microchip P-QS laser.

Referring to method 1100 as a whole, it is noted that optionally one orboth of the SAC and the GMC (and optionally one or more intermediateconnecting crystalline materials, if any) are transparent to therelevant wavelengths (e.g., SWIR radiation).

FIGS. 11B and 11C include several conceptual timelines for the executionof method 1100, in accordance with examples of the presently disclosedsubject matter. To simplify the drawing, it is assumed that the SA is aresult of the processing of the at least one first powder, and that thegain medium is a result of the processing of the at least one secondpowder. As mentioned above, the roles may be reversed.

FIG. 12B shows schematically another example of a PS numbered 1200′,which is an example of PS 1200. In PS 1200′, other components 1206 arein the form of a “3T” (three-transistor) structure. Any other suitablecircuitry may serve as additional components 1206.

Current source 1204 may be used to provide a current of the samemagnitude but of opposite direction to the dark current generated by PD1202, thereby cancelling the dark current (or at least reducing it).This is especially useful if PD 1202 is characterized by high darkcurrent. This way, the charge which flows from the PD to a capacitance(which, as aforementioned, may be provided by one or more capacitors, byparasitic capacitance of the PS, or by a combination thereof) and thecharge that results from the dark current can be canceled out. Notably,providing by current source 1204 of a current which is substantiallyequal in magnitude to the dark current means that the provided currentdoes not cancel out the actual electric signal generated by PD 1202 as aresult of detected light impinging on PD 1202.

FIG. 13A shows a PDD 1300 in accordance with examples of the presentlydisclosed subject matter. PDD 1300 includes circuitry that cancontrollably match the current issued by current source 1204 to the darkcurrent generated by PD 1202, even in cases in which the generated darkcurrent is not constant (changes with time). It is noted that the levelof dark current generated by PD 1202 may depend on different parameterssuch as operational temperature and the bias applied to the PD (whichmay also change from time to time).

The reducing of the effects of dark current within PS 1200 as done byPDD 1300 (and not in later stages of signal processing, either analog ordigital), enable utilization of a relatively small capacitance, withoutsaturating the capacitance or reducing the linearity of its response tothe collected charge.

PDD 1300 comprises a PS 1200 for detecting impinging light, and areference PS 1310 whose outputs are used by additional circuitry(discussed below) for reducing or eliminating effects of dark current inPS 1200. Like PS 1200 (and 1200′), reference PS 1310 includes a PD 1302,a VCCS 1304 and, optionally, additional circuitry (“other components”,collectively denoted 1306). In some examples, reference PS 1310 of PDD1300 may be identical to PS 1200 of PDD 1300. Optionally, any one ormore components of PS 1310 may be identical to a corresponding componentof PS 1200. For example, PD 1302 may be substantially identical to PD1202. For example, VCCS 1304 may be identical to VCCS 1204. Optionally,any one or more components of PS 1310 may differ from those of PSs 1200(e.g., PDs, current source, additional circuitry). It is noted thatsubstantially identical components of PS 1200 and of PS 1310 (e.g., PDs,current source, additional circuitry) may be operated in differentoperational conditions. For example, different biases may be applied toPDs 1202 and 1302. For example, different components of additionalcomponents 1206 and 1306 may be operated using different parameters, orselectively connected/disconnected, even when their structure issubstantially identical. For the sake of simplicity and clarity,components of PS 1310 are numbered with numerals 1302 (for the PD), 1304(for the VCCS) and 1306 (for the additional circuitry), without implyingthat this indicates such components are different from components 1202,1204 and 1206.

In some examples, reference additional circuitry 1306 may be omitted ordisconnected, so as to not affect the determination of the dark current.PD 1202 may operate at one of: reverse bias, forward bias, zero bias, orselectively between any two or three of the above biases (e.g.,controlled by a controller such as controller 1338 discussed below). PD1302 may operate at one of: reverse bias, forward bias, zero bias, orselectively between any two or three of the above biases (e.g.,controlled by a controller such as controller 1338 discussed below). PDs1202 and 1302 may operate under substantially the same bias (e.g., about−5V, about 0V, about +0.7V), bus this is not necessarily so (e.g., whentesting PDD 1300, as discussed below in greater detail). Optionally, asingle PS of PDD 1300 may operate at some times as PS 1200 (detectinglight from a field of view (FOV) of PDD 1300) while in other time as PS1310 (whose detection signal outputs are used for determining a controlvoltage for a VCCS of another PS 1200 of the PDD). Optionally, the rolesof the “active” PS used for detecting impinging light and of thereference PS may be exchanged. PDD 1300 further comprises acontrol-voltage generating circuitry 1340 that includes at leastamplifier 1318 and electrical connections to multiple PSs of PDD 1300.Amplifier 1318 has at least two inputs: first input 1320 and secondinput 1322. First input 1320 of amplifier 1318 is supplied with afirst-input voltage (V_(FI)) which may be directly controlled bycontroller (implemented on PDD 1300, on an external system, or incombination thereof), or derived from other voltages in the system(which may, in turn, be controlled by the controller). Second input 1322of amplifier 1318 is connected to the cathode of PD 1302 (of referencePS 1310).

In a first use case example, PD 1202 is maintained at a working bias,between a first voltage (also referred to as “anode voltage”, denotedV_(A)) and a second voltage (also referred to as “cathode voltage”,denoted V_(C)). The anode voltage may be directly controlled by thecontroller (implemented on PDD 1300, on an external system, or incombination thereof), or derived from other voltages in the system(which may, in turn, be controlled by the controller). The cathodevoltage may be directly controlled by the controller (implemented on PDD1300, on an external system, or in combination thereof), or derived fromother voltages in the system (which may, in turn, be controlled by thecontroller). Each of the anode voltage V_(A) and the cathode voltageV_(C) may or may not be kept constant in time. For example, the anodevoltage V_(A) may be provided by a constant source (e.g., via a pad,from an external controller). The cathode voltage V_(C) may besubstantially constant or changing with time, depending on theimplementation. For example, when using a 3T structure for PS 1200,V_(C) changes with time, e.g., due to operation of additional components1206 and/or to current from PD 1202. V_(C) may optionally bedetermined/controlled/affected by additional components 1206 (and not bythe reference circuit).

VCCS 1204 is used to provide (feed) a current to the cathode end of PD1202 to counter dark current generated by PD 1202. It is noted that atother times, VCCS 1204 may feed other current to achieve other ends(e.g., for calibrating or testing PDD 1300). The level of the currentgenerated by VCCS 1204 is controlled in response to an output voltage ofamplifier 1318. The control voltage for controlling VCCS 1204, denotedV_(CTRL), may be identical to an output voltage of amplifier 1318 (asillustrated). Alternatively, V_(CTRL) may be derived from the outputvoltage of amplifier 1318 (e.g., due to resistance or impedance betweenthe output of amplifier 1318 and VCCS 1204.

To cancel out (or at least reduce) the effect of the dark current of PD1202 on the output signal of PS 1200, PDD 1300 may subject PD 1302 tosubstantially the same bias to which PD 1202 is subjected. For example,subjecting PD 1302 and PD 1202 to the same bias may be used when PD 1302is substantially identical to PD 1202. One way to apply the same bias toboth PDs (1202 and 1302) is to apply voltage V_(A) to the anode of PD1302 (where the voltage applied is denoted V_(RPA), RPA standing for“reference PD anode”), and to apply voltage V_(C) to the cathode of PD1302 (where the voltage applied is denoted V_(RPC), RPC standing for“reference PD cathode”). Another way of applying the same bias is applyV_(RPA)=V_(A)+ΔV to the anode of PD 1302 and V_(RPC)=V_(C)+ΔV to thecathode of PD 1302. Optionally, anode voltage V_(A), reference anodevoltage V_(RPA), or both may be provided by an external source (e.g.,via a printed circuit board (PCB) to which PDD 1300 is connected).

As mentioned, first input 1320 of amplifier 1318 is supplied withfirst-input voltage V_(FI). Second input 1322 of amplifier 1318 isconnected to the cathode of PD 1302. Operation of amplifier 1318 reducesdifferences in voltage between its two inputs (1320 and 1322), therebybringing the voltage on second input 1322 towards the same controlledvoltage which is applied to the first-input (V_(FI)). Refer now to FIG.3B, in which the dark current over PD 1302 (hereinbelow denotedDC_(Reference)) is represented by an arrow 1352 (the illustrated circuitis identical to that of FIG. 3A). The current over PD 1302 is equal tothe dark current of PD 1202 in the case PD 1202 is kept in the darkduring that time. PDD 1300 (or any system component connected oradjacent to it) may block light to PD 1302, so it is kept in the dark.The blocking may be by a physical barrier (e.g., opaque barrier), byoptics (e.g., diverting lenses), by electronic shutter, and so on. Inthe explanation below it is assumed that all current on PD 1302 is darkcurrent generated by PD 1302. Alternatively, if PD 1302 is subjected tolight (e.g., low levels of known stray light in the system), a currentsource may be implemented to offset the known light-originating signal,or the first-input voltage V_(FI) may be amended to compensate (at leastpartly) for the stray illumination. The barrier, optics, or otherdedicated components intended to keep light away from PD 1302 may beimplemented on the wafer level (on the same wafer from which PDD 1300 ismade), may be connected to that wafer (e.g., using adhesive), may berigidly connected to a casing in which the wafer is installed, and soon.

Assuming V_(FI) is constant (or changes slowly), the output of VCCS 1304(represented by arrow 1354) has to be substantially equal in magnitudeto the dark current of PD 1302 (DC_(Reference)), which means VCCS 1304provides the charge carriers for the dark current consumption of PD1302, thus allowing the voltage to remain at V_(FI). Since the output ofVCCS 1304 is controlled by V_(CTRL) which is responsive to the output ofamplifier 1318, amplifier 1318 is operated to output the required outputsuch that V_(CTRL) would control the current output by VCCS 1304 whichwould be identical in magnitude to the dark current over PD 1302.

If PD 1202 is substantially identical to PD 1302 and VCCS 1204 issubstantially identical to VCCS 1304, the output of amplifier 1318 wouldalso cause VCCS 1204 to provide the same level of current(DC_(Reference)) to the cathode of PD 1202. In such a case, for theoutput of VCCS 1204 to cancel out the dark current generated by PD 1202(hereinbelow denoted DC_(ActivePD)), it is required that both PD 1202and PD 1302 would generate a similar level of dark current. To subjectboth PDs (1202 and 1302) to the same bias (which would cause both PDs togenerate substantially the same level of dark current, as both PDs aremaintained in substantially the same conditions, e.g., temperature), thevoltage provided to the first input of amplifier 1318 is determined inresponse to the anode voltage and the cathode voltage of PD 1202, and tothe anode voltage of PD 1302. For example, if V_(A) is equal to V_(RPA),then V_(FI) which is equal to V_(C) may be provided to first input 1320.It is noted that V_(C) may change with time, and is not necessarilydetermined by a controller (for example, V_(C) may be determined asresult of additional components 1206). If PD 1202 differs from PD 1302and/or if VCCS 1204 differs from VCCS 1304, the output of amplifier 1318may be modified by matching electric components (not shown) betweenamplifier 1318 and VCCS 1204 to provide the relevant control voltage toVCCS 1204 (e.g., if it is known that the dark current over PD 1202 islinearly correlated to the dark current over PD 1302, the output ofamplifier 1318 may be modified according to the linear correlation).Another way of applying the same bias is to apply V_(RPA)=V_(A)+ΔV tothe anode of PD 1302 and V_(RPC)=V_(C)+ΔV to the cathode of PD 1302.

FIG. 13C shows a photodetecting device 1300′ that includes a pluralityof PSs 1200, in accordance with examples of the presently disclosedsubject matter. PDD 1300′ includes all of the components of PDD 1300, aswell as additional PSs 1200. The different PSs of PDD 1300′ aresubstantially identical to one another (e.g., all are part of atwo-dimensional PDA), and therefore the PDs 1302 of the different PSs1200 generate similar dark current as one another. Therefore, the samecontrol voltage V_(CTRL) is supplied to all of the VCCSs 1204 of thedifferent PSs 1200 of PDD 1300′, causing these VCCSs 1204 to cancel out(or at least reduce) the effects of the dark current generated by therespective PDs 1202. Any option discussed above with respect to PDD 1300may be applied, mutatis mutandis, to PDD 1300′.

In some cases (e.g., if V_(C) is not constant and/or is not known), itis possible to provide a first-input voltage V_(FI) (e.g., by acontroller) which is selected to cause a similar dark current on PD 1302as on PD 1202.

Refer now to FIG. 14, which shows an exemplary PD I-V curve 1400 inaccordance with examples of the presently disclosed subject matter. Forsimplicity of explanation, curve 1400 represents the I-V curves of bothPD 1302 and PD 1202, which are assumed to be substantially identical forthe purpose of the present explanation, as well as subject to the sameanode voltage (i.e., for this explanation, V_(A)=V_(RPA)). I-V curve1400 is relatively flat between voltages 1402 and 1404, which meansdifferent biases between 1402 and 1404 which are applied to the relevantPD would yield similar levels of dark current. If V_(C) is changingwithin a cathode voltage range which, given a known V_(A), means thebias on PD 1202 is confined between voltages 1402 and 1404, thenapplying a V_(RPC) which causes the bias on PD 1302 to also be betweenvoltages 1402 and 1404 would cause VCCS 1204 to output a current whichis sufficiently similar to DC_(ActivePD), even though PD 1202 and PD1302 are subject to different biases. The V_(RPC) in such case may bewithin the cathode voltage range—as exemplified by equivalent voltage1414, or outside it (but still maintaining the bias on PD 1302 between1402 and 1404—as exemplified by equivalent voltage 1412. Modificationsto other configurations, such as those discussed above, may beimplemented, mutatis mutandis. It is noted that different biases may beapplied to different PDs 1202 and 1302 for other reasons as well. Forexample, different biases may be applied as part of testing orcalibrating of the PDA.

In real life, different PDs (or other components) of different PSs of asingle PDD are not manufactured exactly identically, and the operationof this PSs is also not exactly identical to one another. In a PD array,PDs may be somewhat different from one another and may have somewhatdifferent dark currents (e.g., because manufacturing differences, slightdifference in temperatures, etc.).

FIG. 15 shows a control-voltage generating circuitry 1340 connected to aplurality of reference photosites 1310 (collectively denoted 1500), inaccordance with examples of the presently disclosed subject matter. Thecircuit of FIG. 15 (also referred to as reference circuit 1500) may beused for determining a control voltage (denoted V_(CTRL)) for one ormore VCCSs 1204 of corresponding one or more PSs 1310 of PDDs 1300,1300′, and any of the PDD variations discussed in the presentdisclosure. Especially, reference circuit 1500 may be used fordetermining a control voltage for canceling out (or limiting) theeffects of dark current in one or more PSs 1200 of a PDD based on datacollected from a plurality of reference PSs 1310 which are varying tosome extent (e.g., as a result of manufacturing inaccuracies, somewhatdifferent operational conditions, etc.). As aforementioned, darkcurrents of PDs, even if similar, may be different from one another. Itis noted that in some PD technologies, PDs intended to be identical mayfeature dark currents that are different by a factor of ×1.5, ×2, ×4,and even more. The averaging mechanism discussed herein allows tocompensate for even such significant divergences (e.g., in manufacture).In cases amplifier 1318 is connected to a plurality of reference PSs1310 for averaging dark current levels of several PSs 1310, such PSs1310 are kept in the dark, e.g., using any of the mechanisms discussedabove. The voltages applied to the different VCCSs 1304 of the variousPSs 1310 are short-circuited such that all of the VCCSs 1304 receivesubstantially the same control voltage. The cathode voltages of thedifferent reference PDs 1302 are short-circuited to different nets. Thisway, while the currents in the different reference PSs 1310 are somewhatdifferent from one another (resulting from reference PSs 1310 beingslightly different from one another), the average control voltagesupplied to the one or more PSs 1200 of the respective PDD (which mayalso somewhat differ from one another and from reference PSs 1310) issufficiently accurate for canceling out the effects of dark current onthe different PSs 1200, and in a sufficiently uniform manner.Optionally, the output voltage of a single amplifier 1318 is supplied toall PSs 1200 and to all reference PSs 1310. Optionally, the selected PDsfor the PDD have a flat I-V response (as discussed above, e.g., withrespect to FIG. 14), such that the average control voltage discussedwith respect to reference circuitry 1500 cancels out the dark current inthe different PSs 1200 to a very good degree. Non-limiting examples ofPDDs which include multiple reference PSs 1310 whose averaged outputsignals are used for modifying the output signals of multiple active PSs1200 (e.g., to reduce effects of dark current of output signal) areprovided in FIGS. 16A and 16B. Different configurations, geometries, andnumerical ratios may be implemented between the reference PSs 1310 andthe active PSs 1200 of a single PDD. For example, in a rectangularphotodetecting array that includes a plurality of PSs arranged in rowsand columns, an entire row of PSs (e.g., 1,000 PSs) or a few rows orcolumns of PSs may be used as the plurality of reference PSs 1310 (andoptionally kept in the dark), while the rest of the array receives thecontrol signal that is based on averaging the outputs of those referencePS rows. This way of generating control current greatly reduces theeffects of dark current by removing the average dark current, leavingonly PS-to-PS variations.

FIGS. 16A and 16B show photodetecting devices that comprise an array ofPSs and reference circuitry which is based on a plurality of PDs, inaccordance with examples of the presently disclosed subject matter. PDD1600 (illustrated in FIG. 16A) and PDD 1600′ (illustrated in FIG. 16B,which is a variation of PDD 1600) include all of the components of PDD1300, as well as additional PSs 1200 and PSs 1310. Optionally, thedifferent PSs of PDD 1600 (and, separately, of PDD 1600′) aresubstantially identical to one another. Any option discussed above withrespect to PDDs 1300 and 1300′ as well as with respect to circuit 1500may be applied, mutatis mutandis, to PDDs 1600 and 1600′.

FIG. 16A shows a photodetector device 1600 comprising a photosensitivearea 1602 (which is exposed to external light during operation ofphotodetector device 1600) with a plurality (array) of PSs 1200, an area1604 with a plurality of reference PSs 1310 that are kept in the dark(at least during reference current measurements, optionally at alltimes), and control-voltage generating circuitry 1340 which furtherincludes controller 1338. Controller 1338 may control operation ofamplifier 1318, voltages that are supplied to amplifier 1318, and/oroperation of reference PSs 1310. Optionally, controller 1338 may alsocontrol operations of PSs 1200 and/or of other components of PDD 1600.Controller 1338 may control both active PSs 1200 and reference PSs 1310to operate under the same operational conditions (e.g., bias, exposuretime, managing readout regimes). It is noted that any functionality ofcontroller 1338 may be implemented by an external controller (e.g.,implemented on another processor of an EO system in which the PDD isinstalled, or by an auxiliary system such as a controller of anautonomous vehicle in which the PDD is installed). Optionally,controller 1338 may be implemented as one or more processors fabricatedon the same wafer as other components of PDD 1600 (e.g., PSs 1200 and1310, amplifier 1318). Optionally, controller 1338 may be implemented asone or more processors on a PCB connected to such a wafer. Othersuitable controllers may also be implemented as controller 1338.

FIG. 16B shows a photodetector device 1600′ in accordance with examplesof the presently disclosed subject matter. Photodetector device 1600′ issimilar to device 1600, but with the components are arranged in adifferent geometry and without showing internal details of the differentPSs. Also illustrated is readout circuitry 1610 which is used to readthe detection signals from PSs 1200 and to provide them for furtherprocessing (e.g., to reduce noise, for image processing), for storage,or for any other use. For example, readout circuitry 1610 may temporallyarrange the readout values of the different PSs 1200 sequentially(possibly after some processing by one or more processors of the PDD,not shown) before providing them for further processing, storage, or anyother action. Optionally, readout circuitry 1610 may be implemented asone or more units fabricated on the same wafer as other components ofPDD 1600 (e.g., PSs 1200 and 1310, amplifier 1318). Optionally, readoutcircuitry 1610 may be implemented as one or more units on a PCBconnected to such a wafer. Other suitable readout circuitries may alsobe implemented as readout circuitry 1610. It is noted that a readoutcircuitry such as readout circuitry 1610 may be implemented in any ofthe photodetecting devices discussed in the present disclosure (e.g.,PDDs 1300, 1700, 1800, and 1900). Examples for analog signal processingthat may be executed in the PDD (e.g., by readout circuitry 1610 or byone or more processors of the respective PDD) prior to an optionaldigitization of the signal include: modifying gain (amplification),offset and binning (combining output signals from two or more PSs).Digitization of the readout data may be implemented on the PDD orexternal thereto.

Optionally, PDD 1600 (or any of the other PDDs disclosed in the presentdisclosure) may include a sampling circuitry for sampling the outputvoltage of amplifier 1318 and/or the control voltage V_(CTRL) (ifdifferent), and for holding that voltage level for at least a specifiedminimum period of time. Such sampling circuitry may be positioned at anyplace between the output of amplifier 1318 and one or more of the atleast one VCCSs 1204 (e.g., at location 1620). Any suitable samplingcircuitry may be used; for example, in some cases, exemplary circuitrymay include “sample and hold” switches. Optionally, the samplingcircuitry may be used only some of the times, and direct real-timereadout of the control voltage is executed in other times. Using asampling circuitry may be useful, for example, when the magnitudes ofdark currents in the system change slowly, when PSs 1310 are shieldedfrom light only at parts of the times.

FIGS. 17 and 18 show more photodetecting devices in accordance withexamples of the presently disclosed subject matter. In thephotodetecting devices described above (e.g., 1300, 1300′, 1600, 1600′),a voltage-controlled current source was used for both of the active PSs1200 and the reference PSs 1310. A current source is one example of avoltage-controlled current-circuit which may be used in the disclosedPDD. Another type of voltage-controlled current-circuit which may beused is voltage-controlled current-sink, which absorbs current inmagnitude which is controlled by the control voltage supplied to it. Acurrent sink may be used, for example, in which the bias over the PDs(1202, 1302) is opposite in direction to the bias exemplified above.More generally, whenever a voltage-controlled current source isdiscussed above (1204, 1304), this component may be replaced by avoltage-controlled current sink (denoted, respectively, 1704 and 1714).It is noted that using a current sink instead of a current source mayrequire using different types of components or circuits in other partsof the respective PDD. For example, an amplifier 1318 which is usedtogether with VCCSs 1204 and 1304 is different in power, size, etc. thanamplifier 1718 which is used together with voltage-controlled currentsinks 1704 and 1714. To differentiate PSs which includevoltage-controlled current sinks rather than VCCSs, the referencenumbers 1200′ and 1310′ are used correspondingly to PSs 1200 and 1300discussed above.

In FIG. 17, a PDD 1700 includes voltage-controlled current circuits thatare voltage-controlled current sinks (in both PS 1200′ and PS 1310′),and a suitable amplifier 1718 is used instead of amplifier 1318. Allvariations discussed above regarding current sources are equallyapplicable to current sinks.

In FIG. 18, a PDD 1800 includes both types of voltage-controlled currentcircuits—both voltage-controlled current sources 1204 and 1314 andvoltage-controlled current sinks 1704 and 1714, with matching amplifiers1318 and 1718. This may allow, for example, operating the PDs of PDD1800 in either forward or reverse bias. At least one switch (or otherselection mechanisms) may be used to choose which of the referencecircuits is activated/deactivated—the one based on VCCSs or the onebased on voltage-controlled current sinks. Such selection mechanism maybe implemented, for example, to prevent the two feedback regulatorsworking “against” one another (e.g., if working in near-zero biases overthe PDs). Any option, explanation or variation discussed above withrespect to any of the previously discussed PDDs (e.g., 1300, 1300′,1600, 1600′) may be applied, mutatis mutandis, to PDDs 1700 and 1800.Especially, PDDs 1700 and 1800 may include a plurality of PSs 1200′and/or a plurality of reference PSs 1310′, similar to the discussionsabove (e.g., with respect to FIGS. 15, 16A, and 16B).

It is noted that in any of the photodetecting devices discussed above,one or more of the PSs (e.g., of a photodetecting array) may optionallybe controllable to be used selectively as a reference PS 1310 (e.g. atsome times) or as a regular PS 1200 (e.g. at other times). Such PSs mayinclude the required circuitry for operating in both roles. This may beused, for example, if the same PDD is used in different types ofelectro-optical systems. For example, one system may require theaccuracy of averaging between 1,000 and 4,000 reference PSs 1310 whileanother system may require a lower accuracy which may be achieved byaveraging between 1 and 1200 reference PSs 1310. In another example,averaging of control voltage based on some (or even all) of the PSs maybe executed when the entire PDA is darkened and stored in asample-and-hold circuitry as discussed above, and all of the PSs may beused for detection of FOV data using the determined control voltage inone or more following frames.

It is noted that in the discussion above, it was assumed for the sake ofsimplicity that the anode side of all PDs on the respective PDA areconnected to a known (and possibly controlled) voltage, and thedetection signals as well as connection of VCCSs and additionalcircuities is implemented on the cathode side. It is noted thatoptionally, the PDs 1202 and 1302 may be connected the opposite way(where the readout is on the anode side, and so on), mutatis mutandis.

Referring to all of the PDDs discussed above (e.g., 1300, 1600, 1700,1800), it is noted that the PSs, the readout circuitry, the referencecircuitry and the other aforementioned components (as well anyadditional components that may be required) may be implemented on asingle wafer or on more than one wafer, on one or more PCBs or anothersuitable type of circuit connected to the PSs, and so on.

FIG. 19 illustrates a PDD 1900, in accordance with examples of thepresently disclosed subject matter. PDD 1900 may implement anycombination of features from any one or more of the PDDs describedabove, and further include additional components. For example, PDD 1900may include any one or more of the following components:

-   -   a. at least one light source 1902, operative to emit light onto        the FOV of PDD 1900. Some of the light of light source 1902 is        reflected from objects in the FOV and is captured by PSs 1200 in        photosensitive area 1602 (which is exposed to external light        during operation of photodetector device 1900) and is used to        generated an image or another model of the objects. Any suitable        type of light source may be used (e.g., pulsed, continuous,        modulated, LED, laser). Optionally, operation of light source        1902 may be controlled by a controller (e.g., controller 1338).    -   b. a physical barrier 1904 for keeping area 1604 of the detector        array in the dark. Physical barrier 1904 may be part of the        detector array or external thereto. Physical barrier 1904 may be        fixed or movable (e.g., a moving shutter). It is noted that        other type of darkening mechanisms may also be used. Optionally,        physical barrier 1904 (or other darkening mechanism) may darken        different parts of the detection array in different times.        Optionally, operation of barrier 1904, if changeable, may be        controlled by a controller (e.g., controller 1338).    -   c. ignored photosites 1906. It is noted that not all PSs of the        PDA are necessarily used for either detection (PSs 1200) or as        reference (PSs 1310). For example, some PSs may reside in an        area that is not entirely darkened and not entirely lit, and are        therefore ignored in the generation of the image (or other type        of output generated in response to the detection signals of PSs        1200). Optionally, different PSs may be ignored at different        times by PDD 1900.    -   d. at least one processor 1908 for processing the detection        signals output by PSs 1200. Such processing may include, for        example, signal processing, image processing, spectroscopy        analysis, and so on. Optionally, processing results by processor        1908 may be used for modifying operation of controller 1338 (or        another controller). Optionally, controller 1338 and processor        1908 may be implemented as a single processing unit. Optionally,        processing results by processor 1908 may be provided to any one        or more of: a tangible memory module 1910 (for storage or later        retrieval, see next), for external systems (e.g., a remote        server, or a vehicle computer of a vehicle in which PDD 1900 is        installed), e.g., via a communication module 1912, a display        1914 for displaying an image or other type of result (e.g.,        graph, textual results of spectrograph), another type of output        interface (e.g. a speaker, not shown), and so on. It is noted        that optionally, signals from PSs 1310 may also be processed by        processor 1908, for example to assess a condition of PDD 1900        (e.g., operability, temperature).    -   e. a memory module 1910 for storing at least one of detection        signals output by the active PSs or by readout circuitry 1610        (e.g., if different), and detection information generated by        processor 1908 by processing the detection signals.    -   f. power source 1916 (e.g., battery, AC power adapter, DC power        adapter). The power source may provide power to the PSs, to the        amplifier, or to any other component of the PDD.    -   g. a hard casing 1918 (or any other type of structural support).    -   h. optics 1920 for directing light of light source 1902 (if        implemented) to the FOV and/or for directing light from the FOV        to the active PSs 1200. Such optics may include, for example,        lenses, mirrors (fixed or movable), prisms, filters, and so on.

As aforementioned, the PDDs described above can be used for matching thecontrol voltage determining the level of current provided by the atleast one first voltage controlled current circuits (VCCCs) 1204 toaccount for differences in operation conditions of the PDD, which changethe levels of dark current generated by the at least one PD 1202. Forexample, for a PDD that includes a plurality of PSs 1200 and a pluralityof PSs 1320: when the PDD operates at a first temperature,control-voltage generating circuitry 1340 provides to the voltagecontrolled current circuit a control voltage for providing a current ata first level in response to dark currents of the plurality of referencePDs 1302, to reduce effect of dark currents of the active PDs 1202 onoutput of active PSs 1200; and when the PDD operates at a secondtemperature (higher than the first temperature), control-voltagegenerating circuitry 1340 provides to the voltage controlled currentcircuit a control voltage for providing a current at a second level inresponse to dark currents of the plurality of reference PDs 1302, toreduce effect of dark currents of the active PDs 1202 on output ofactive PSs 1200, such that the second level is larger in magnitude thanthe first level.

FIG. 20 is a flow chart of method 2000 for compensating for dark currentin a photodetector, in accordance with examples of the presentlydisclosed subject matter. Method 2000 is executed in a PDD that includesat least: (a) a plurality of active PSs, each including at least oneactive PD; (b) at least one reference PS that includes a reference PD;(c) at least one first VCCC connected to one or more active PDs; (d) atleast one reference VCCC connected to one or more reference PDs; and (e)a control-voltage generating circuitry that is connected to the activeVCCC and to the reference VCCC. For example, method 2000 may be executedin any of PDDs 1300′, 1600, 1600′, 1700, and 1800 (the latter two inimplementations which include a plurality of active PSs). It is notedthat method 2000 may include executing any action or function discussedabove with respect to any component of the various aforementioned PDDs.

Method 2000 includes at least stages (stages) 2010 and 1020. Stage 2010includes: based on a level (or levels) of dark current in the at leastone reference PD, generating a control voltage that, when provided tothe at least one reference VCCC causes the at least one reference VCCCto generate a current that reduces an effect of dark current of thereference PD on an output of the reference PS. Stage 2020 includesproviding the control voltage to the at least one first VCCC, therebycausing the at least one first VCCC to generate a current that reducesan effect of dark current of the active PDs on outputs of the pluralityof active PSs. VCCC stands for “Voltage Controlled Current Circuit”, andit is implemented either as a voltage-controlled current source or as avoltage-controlled current sink.

Optionally, stage 2010 is implemented using an amplifier that is a partof the control-voltage generating circuitry. In such a case, stage 2010includes supplying to a first input of the amplifier a first inputvoltage when a second input of the amplifier is electrically connectedbetween the reference PD and the reference voltage controlled currentcircuit. The amplifier may be used to continuously reduce a differencebetween an output of the reference voltage-controlled circuit and thefirst input voltage, thereby generating the control voltage. Optionally,both the first VCCC(s) and the reference VCCC(s) are connected to anoutput of the amplifier.

In case the PDD includes a plurality of different reference PDs thatgenerate different levels of dark current, stage 2010 may includegenerating a single control voltage based on averaging of the differingdark currents of the reference PDs.

Method 2000 may include preventing light from a field of view of the PDDfrom reaching the reference PDs (e.g., using a physical barrier ordiverting optics).

Method 2000 may include sampling outputs of the active PSs after thereduction of the effects of dark current, and generating an image basedon the sampled outputs.

FIG. 21 is a flow chart illustrating a method 1020 for compensating fordark current in a photodetecting device, in accordance with examples ofthe presently disclosed subject matter. Method 1020 have two phaseswhich are executed in different temperature regimes; a first group ofstages (1110-1116) is executed when the PDD operates in a firsttemperature (T₁), and a second group of stages (1120-1126) is executedwhen the PDD operates in a second temperature (T₂) which is higher thanthe first temperature. The degree by which the first temperature and thesecond temperature may be different in different implementations or indifferent instances of method 1200. For example, the temperaturedifference may be at least 5° C.; at least 10° C.; at least 20° C.; atleast 40° C.; at least 100° C., and so on. Notably, method 1020 may beeffective in even smaller temperature differences (e.g., less than 1°C.). It is noted that each of the first temperature and the secondtemperature may be implemented as a temperature range (e.g., spanning0.1° C.; 1° C.; 5° C., or more). Any temperature in the secondtemperature range is higher than any temperature in the firsttemperature range (e.g., by the ranges mentioned before). Method 2000may optionally be executed in any of the PDDs discussed above (1300,1600, etc.). It is noted that method 1020 may include executing anyaction or function discussed above with respect to any component of thevarious aforementioned PDDs, and that the PDD of method 1020 may includeany combination of one or more of the components discussed above withrespect to any one or more of the aforementioned PDDs.

Referring to stages carried out when the PDD operates in the firsttemperature (which may be a first temperature range): Stage 2110includes determining a first control voltage based on dark current of atleast one reference PD of the PDD. Stage 2112 includes providing thefirst control voltage to a first VCCC which is coupled to at least oneactive PD of an active PS of the PDD, thereby causing the first VCCC toimpose a first dark-current countering current in the active PS. Stage2114 includes generating by the active PD a first detection current inresponse to: (a) light impinging of the active PD originating in anobject in a field of view of the PDD, and (b) dark current generated bythe active PD. Stage 2116 includes outputting by the active PS a firstdetection signal whose magnitude is smaller than the first detectioncurrent in response to the first detection current and to the firstdark-current countering current, thereby compensating effect of darkcurrent on the first detection signal. Method 1020 may also includeoptional stage 2118 of generating at least one first image of a FOV ofthe PDD based on a plurality of first detection signals from a pluralityof PSs of the PDD (and optionally all of them). Stage 2118 may beexecuted when the PDD is at the first temperature, or at a later stage.

Referring to stages carried out when the PDD operates in the secondtemperature (which may be a second temperature range): Stage 2120includes determining a second control voltage based on dark current ofat least one reference PD of the PDD. Stage 2122 includes providing thesecond control voltage to the first VCCC, thereby causing the first VCCCto impose a second dark-current countering current in the active PS;Stage 2124 includes generating by the active PD a second detectioncurrent in response to: (a) light impinging of the active PD originatingin the object, and (b) dark current generated by the active PD. Stage2126 includes outputting by the active PS a second detection signalwhose magnitude is smaller than the second detection current in responseto the second detection current and to the second dark-currentcountering current, thereby compensating effect of dark current on thesecond detection signal. A magnitude of the second dark-currentcountering current is larger than a magnitude of the first dark-currentcountering current, and could be by any ratio larger than one. Forexample, the ration may be by a factor of at least two, or significantlyhigher (e.g., by one, two, three—or more—orders of magnitude). Method1020 may also include optional stage 2128 of generating at least onesecond image of a FOV of the PDD based on a plurality of seconddetection signals from a plurality of PSs of the PDD (and optionally allof them). Stage 2128 may be executed when the PDD is at the secondtemperature, or at a later stage.

Optionally, a first level of radiation (L₁) from the object impinging onthe active PD during a first time (t₁) at which the first dark-currentcountering current is generated is substantially equal to a second levelof radiation (L₂) from the object impinging on the active PD during asecond time (t₂) at which the second dark-current countering current isgenerated, wherein a magnitude of the second detection signal issubstantially equal to a magnitude of the first detection signal. Itshould be noted that optionally, the PDD according to the presentdisclosure can be used to detect signal levels which are significantlylower than the levels of dark current generated its PDs at certainoperational temperatures (e.g., by one, two or more orders ofmagnitude). Therefore, method 1020 may be used to issue similar levelsof output signals in two different temperatures, in which the darkcurrents are two or more order of magnitudes larger than the detectionsignals, and significantly different than one another (e.g., by a factor×2, ×10)

Optionally, the determining of the first control voltage and thedetermining of the second control voltage are executed by acontrol-voltage generating circuitry that includes at least oneamplifier having an input electrically connected between the referencePD and a reference voltage controlled current circuit which is coupledto the reference PD.

Optionally, method 1020 may further include supplying to another inputof the amplifier a first-input voltage whose level is determinedcorresponding to a bias on the active PD. Optionally, method 1020 mayinclude supplying the first input voltage such that a bias on thereference PD is substantially the same as a bias on the active PD.Optionally, method 1020 may include determining the first controlvoltage and the second control voltage based on differing dark currentsof a plurality of reference PDs of the PDD, wherein the providing of thefirst control voltage includes providing the same first control voltageto a plurality of first voltage controlled current circuits, eachcoupled to at least one active PD out of a plurality of active PDs ofthe PDD having differing dark currents, wherein the providing of thesecond control voltage includes providing the same second controlvoltage to the plurality of first voltage controlled current circuits,when the plurality of active PDs are having yet differing dark currents.

Optionally, different active PDs concurrently generate different levelsof dark current, and concurrently different reference PDs generatedifferent levels of dark current, and the control-voltage generatingcircuitry provides to the different active PDs a same control voltagebased on averaging of the differing dark currents of the second PDs.Optionally, method 1020 may include directing light from the field ofview to a plurality of active PSs of the PDD using dedicated optics, andpreventing light from the field of view from reaching a plurality ofreference PDs of the PDD.

FIG. 22 is a flow chart illustrating method 2200 for testing aphotodetecting device, in accordance with examples of the presentlydisclosed subject matter. For example, the testing may be implemented byany of the aforementioned PDDs. That is, the same circuitries andarchitectures which were described above as being useful for reducingthe effects of dark current may be put to additional use, to test thedetection paths of the different PSs in real time. Optionally, thetesting may be done while the PDD is in operational mode (i.e., not intesting mode). In some implementations, some PSs may be tested whileexposed to ambient light from the FOV, and even when other PSs of thesame PDD capture an actual image of the FOV (with or withoutcompensation for dark current). It is nevertheless noted that method2200 may also optionally be implemented in other types of PDDs. It isalso noted that method 2200 may also optionally be implemented usingcircuitries or architectures similar to the ones discussed above withrespect to the aforementioned PDDs, but when the PDs are notcharacterized by high dark current, and when no reduction of darkcurrent is required or carried out. Method 2200 is described as appliedto a single PS, but it may be applied to some or all PSs of a PDD.

Stage 2210 of method 2200 includes providing a first voltage to a firstinput of an amplifier of a control-voltage generating circuitry, whereinthe second input of the amplifier is connected to a reference PD and toa second current circuit which supplies current in a level governed inresponse to an output voltage of the amplifier; thereby causing theamplifier to generate a first control voltage for a first currentcircuit of a PS of the PDD. Referring to the examples set forth withrespect to the previous drawings, the amplifier may be amplifier 1318 oramplifier 1718, and the PS may be PS 1310 or PS 1310′. Examples of whichfirst voltages may be provided to the first input are discussed below.

Stage 2220 of method 2200 includes reading a first output signal of thePS, generated by the PS in response to current generated by the firstcurrent circuit and to current generated by a PD of the PS.

Stage 2230 of method 2200 includes providing to the first input of theamplifier a second voltage which is different than the first input,thereby causing the amplifier to generate a second control voltage forthe first current circuit. Examples of such second voltages may beprovided are discussed below.

Stage 2240 of method 2200 includes reading a second output signal of thePS, generated by the PS in response to current generated by the firstcurrent circuit and to current generated by a PD of the PS.

Stage 2250 of method 2200 includes based on the first output signal andon the second output signal, determining a defectivity state of adetection path of the PDD, the detection path including the PS andreadout circuitry associated with the PS. Examples of which types ofdefects may be detected while using different combinations of firstvoltage and second voltage are discussed below.

A first example includes using at least one voltage out of the firstvoltage and the second voltage to attempt to saturate the PS (e.g., byproviding by the VCCS a very high current to the capacitance of the PS,regardless of the actual detection level). Failing to saturate the PS(e.g., receiving a detection signal which is not white—possiblycompletely black or halftoned) indicates on a problem in the relevantPS, or in further components in its readout path (e.g., PS amplifier,sampler, analog-to-digital converter). In such a case, the first voltage(for example) causes the amplifier to generate a control voltage whichcauses the first current circuit to saturate the PS. The determining ofthe defectivity state at stage 2250 in such a case may includedetermining that the detection path of that PS is malfunctioning inresponse to determining that the first output signal is not saturated.The second voltage in such a case may be one which does not causesaturation of the PS (e.g., which causes the VCCS to issue no current,to compensate for the dark current only, to prevent current from beingcollected by the capacitance). Testing whether a PS detection path canbe saturated can be implemented in real time.

When attempting to saturate one or more of the PSs to test the PDD,method 2200 may include reading the first output signal while the PS isexposed to ambient light during a first detection frame of the PDD,where the determining of the malfunctioning status is executed afterpreviously determining that the detection path is operative in responseto reading a saturated output signal at a second detection frame whichis earlier than the first frame. For example, during an ongoingoperation of the PDD (e.g., while capturing a video), a PS may bedetermined as defective or unusable if saturation attempt failed, afterit succeeded at a previous time during the same operation. The testingmay be executed at a testing frame which is not part of the video, orfor individual PSs whose saturated output is ignored (e.g., the pixelcolor corresponding to these PSs may be completed from neighboringpixels at the frame in which they are tested, treating these PSs asunusable for the span of this frame).

A second example includes using at least one voltage out of the firstvoltage and the second voltage to attempt to deplete the PS (e.g., byproviding by the VCCS a very high opposite current to the capacitance ofthe PS, regardless of the actual detection level). Failing to depletethe PS (e.g., receiving a detection signal which is not black—possiblycompletely white or halftoned) indicates on a problem in the relevantPS, or in further components in its readout path. In such a case, thesecond voltage (for example) causes the amplifier to generate a secondcontrol voltage which causes the first current circuit to deplete adetection signal resulting from field of view light impinging on the PS.The determining of the defectivity state at stage 2250 in such a casemay include determining that the detection path is malfunctioning inresponse to determining that the second output signal is not depleted.The first voltage in such a case may be one which does not causesaturation of the PS (e.g., which causes the VCCS to issue no current,to compensate for the dark current only, to saturate the capacitance).Testing whether a PS detection path can be depleted can be implementedin real time (e.g., without darkening the respective PS).

When attempting to deplete one or more of the PSs to test the PDD,method 2200 may include reading of the second output signal while the PSis exposed to ambient light during a third detection frame of the PDD,wherein the determining of the malfunctioning status is executed afterpreviously determining that the detection path is operative in responseto reading a depleted output signal at a fourth detection frame which isearlier than the third frame.

Yet another example of using method 2200 to test a PS using applying ofmultiple control voltages includes applying more than two voltages. Forexample, three or more different voltages may be provided to the firstinput of the amplifier at different times (e.g., at different frames).In such a case, stage 2250 may include determining the defectivity stateof the detection path of the PDD based on the first output signal, onthe second output signal, and on at least one other output signalcorresponding to the third or more voltages applied to the first inputof the amplifier. For example, three, four, or more different voltagesmay be applied to the first input of the amplifier at different times(e.g., monotonously, where every voltage is greater than a previousvoltage), and the output signals of the same PS corresponding to thedifferent voltages may be tested to correspond to the applied voltages(e.g., the output signals are also monotonously increasing inmagnitude).

An example of using method 2200 to test a portion of a PDD (or even allof it) includes reading from each out of a plurality of PSs of the PDDat least two output signals responsive to at least two differentvoltages provided to the amplifier of the respective PSs, determiningfor at least one first detection path an operative status based on theat least two output signals output by at least one PS associated withthe respective first detection path, and determining for at least onesecond detection path an malfunctioning status based on the at least twooutput signals output by at least one other PS associated with therespective second detection path.

Optionally, method 2200 may be executed in combination with designatedtest targets (e.g., black target, white target), when the PDD isshielded from ambient light, and/or when using designated illumination(e.g., of a known magnitude, of a dedicated internal illumination, andso on), but not necessary so.

Optionally, stage 2250 may be replaced with determining an operationalstate of the detection path. This may be used, for example, to calibratedifferent PSs of the PDD to the same level. For example, when the PDD isdarkened and without a dedicated target or dedicated illumination, thesame voltage may be applied to VCCS of different PSs. the differentoutput signals of the different PSs may be compared to one another (atone or more different voltages applied to the first input of theamplifier). Based on the comparison, correction values may be assignedto the different PSs detection paths, such they would provide a similaroutput signal for similar illumination level (which is simulated by theincluded current by the VCCS s of the different PSs). For example, itmay be determined that the output of PS A should be multiplied by 1.1 tooutput a calibrated output signal to PS B. For example, it may bedetermined that a delta signal ΔS should be added to the output of PS Cto output a calibrated output signal to PS D. nonlinear corrections mayalso be implemented.

FIG. 23 illustrates an EO system 2300, in accordance with examples ofthe presently disclosed subject matter. EO system 2300 includes at leastone PDA 2302 and at least one processor 2304 which is operative toprocess detection signals from PSs 2306 of the PDA. EO system 2300 maybe any type of EO system which uses PDA for detection, such as a camera,a spectrograph, a LIDAR, and so on.

The at least one processor 2304 is operative to and configured forprocessing detection signals output by PSs 2306 of the at least one PDA2302. Such processing may include, for example, signal processing, imageprocessing, spectroscopy analysis, and so on. Optionally, processingresults by processor 2304 may be provided to any one or more of: atangible memory module 2308 (for storage or later retrieval), forexternal systems (e.g., a remote server, or a vehicle computer of avehicle in which EO system 2300 is installed), e.g., via a communicationmodule 2310, a display 2312 for displaying an image or other type ofresult (e.g., graph, textual results of spectrograph), another type ofoutput interface (e.g. a speaker, not shown), and so on.

EO system 2300 may include a controller 2314 which controls operationalparameters of EO system 2300 (e.g., of PDA 2302 and of an optional lightsource 2316). Especially, controller 2314 may be configured to set (orotherwise change) the frame exposure times used for the capturing ofdifferent frames by EO system 2300. Optionally, processing results oflight detection signals by processor 2304 may be used for modifyingoperation of controller 2314. Optionally, controller 2314 and processor2304 may be implemented as a single processing unit.

EO system 2300 may include at least one light source 2316, operative toemit light onto the field of view (FOV) of EO system 2300. Some of thelight of light source 2316 is reflected from objects in the FOV and iscaptured by PSs 2306 (at least those PS which are positioned in aphotosensitive area which is exposed to external light during frameexposure times of EO system 2300). Detection of light arriving fromobjects in the FOV (whether reflection of light source light, reflectionof other light sources, or radiated light) is used to generated an imageor another model (e.g., a three dimensional depth map) of the objects.Any suitable type of light source may be used (e.g., pulsed, continuous,modulated, LED, laser). Optionally, operation of light source 2316 maybe controlled by a controller (e.g., controller 2314).

EO system 2300 may include a readout circuitry 2318 for reading out theelectric detection signals from the different PSs 2306. Optionally,readout circuitry 2318 may process the electric detection signals beforeproviding them to processor 2304. Such pre-processing may include, forexample, amplification, sampling, weighting, denoising, correcting,digitalization, capping, level-adjustments, dark current compensation,and so on).

In addition, EO system 2300 may include additional components such as(but not limited to) any one or more of the following optionalcomponents:

-   -   a. memory module 2308 for storing at least one of detection        signals output by the PSs 2306 or by readout circuitry 2318        (e.g., if different), and detection information generated by        processor 2304 by processing the detection signals.    -   b. a power source 2320 such as a battery, an AC power adapter, a        DC power adapter, and so on. Power source 2320 may provide power        to the PDA, to readout circuitry 2318, or to any other component        of EO system 2300.    -   c. a hard casing 2322 (or any other type of structural support).    -   d. optics 2324 for directing light of light source 2316 (if        implemented) to the FOV and/or for directing light from the FOV        to PDA 2300. Such optics may include, for example, lenses,        mirrors (fixed or movable), prisms, filters, and so on.

Optionally, PDA 2302 may be characterized by relatively high darkcurrent (e.g., as a result of the type and characteristics of its PDs).Because of the high level of dark current, the capacitances of theindividual PSs 2306 in which detection charge is collected may becomesaturated (partly or fully) by the dark current, leaving little to nodynamic range for detection of ambient light (arriving from the FOV).Even if readout circuitry 2318 or processor 2304 (or any other componentof system 2300) subtracts dark current levels from the detection signals(e.g., to normalize the detection data), the lack of dynamic range fordetection means that the resulting detection signal of the respective PS2306 is overly saturated, insufficient for meaningful detection ofambient light levels. Since dark current from the PD of the respectivePS 2306 is accumulated in the capacitance (whether actual capacitor orparasitic or residual capacitance of other components of the PSs) forthe entire duration of the frame exposure time (FET), different PSs 2306with different capacitance may be rendered unusable at different FETs.

FIG. 24 illustrates an example of method 2400 for generating imageinformation based on data of a PDA, in accordance with the presentlydisclosed subject matter. Referring to examples set forth with respectto the previous drawings, method 2400 may be executed by EO system 2300(e.g., by processor 2304, controller 2314, etc.). In such a case, thePDA of method 2400 may optionally be PDA 2302. Other relevant componentsdiscussed in method 2400 may be the corresponding components of EOsystem 2300. Method 2400 includes changing a frame FET (FET) duringwhich the PDA collects charges from its PD. Such collected charge mayresult from photoelectric response to light impinging on the PDs andfrom intrinsic sources within the detection system, such as from darkcurrent of the PD. Impinging light may be arriving, for example, from afield of view (FOV) of a camera or another EO system in which the PDA isinstalled. The FET may be controlled electronically, mechanically, bycontrolling flash illumination duration and so on, or in any combinationthereof.

It is noted that the FET may be an overall FET which is a summation of aplurality of distinct durations during which the PDA collects chargeresulting from photoelectric activity in PSs of the PDA. An overall FETis used in cases charges collected during the different distinctdurations are summed to provide a single output signal. Such overall FETmay be used, for example, with pulsed illumination, or with activeillumination during which collection is withheld for short times (e.g.,to avoid being saturated by a bright reflection in the FOV). It is notedthat optionally in some frames a single FET may be used, while in otherframes an overall FET may be used.

Stage 2402 of method 2400 includes receiving first frame information.The first frame information includes—for each out of a plurality of PSsof a PDA—a first frame detection level indicative of an intensity oflight detected by the respective PS during a first FET. The receiving ofthe first frame information may include receiving readout signals fromall of the PSs of the PDA, but this is not necessarily so. For example,some PSs may be defective and not provide a signal. For example, aregion of interest (ROI) may be defined for the frame, indicating datais to be collected from only a part of the frame, and so on.

The frame information may be provided in any format, such as a detectionlevel (or levels) for each of the PSs (e.g., between 0 and 1024, threeRGB values, each between 0 and 255, and so on), scalar, vector, or anyother formats. Optionally, the frame information (for the first frame orfor later frames) may optionally be indicative of detection signals inindirect manners (e.g., information pertaining to the detection level ofa given PS may be given with respect to the level of a neighboring PS orwith respect to the level of the same PS in a previous frame). The frameinformation may also include additional information (e.g., serialnumber, timestamp, operational conditions), some of which may be used infollowing steps of method 2400. The first frame information (as well asframe information for later frames, received in later stages of method2400) may be received directly from the PDA, or from one or moreintermediary units (such as intermediary processor, memory unit, dataaggregator, and so on). The first frame information (as well as frameinformation for later frames, received in later stages of method 2400)may include the raw data as acquired by the respective PS, but may alsoinclude preprocessed data (e.g., after weighting, denoising, correcting,digitalization, capping, level-adjustments, and so on).

Stage 2404 includes identifying, based on the first FET, at least twotypes of PSs out of the plurality of PSs of the PDD:

a. A group of usable PSs for the first frame (referred to as “firstgroup of usable PSs”), that includes at least a first PS, a second PS,and a third PS of the PSs of the PDA.b. A group of unusable PSs for the first frame (referred to as “firstgroup of unusable PSs”), that includes at least a fourth PS of the PSsof the PDA.

The identifying of stage 2404 may be implemented in different ways, andmay optionally include identifying (explicitly or implicitly) each ofthe pluralities of PSs as belonging to one of the aforementioned atleast two groups. Optionally, each PS of the PDA (or of a previouslydetermined subgroup of it, such as all of the PSs of an ROI) may beassigned to one of the two pluralities with respect to the firstframe—either the first group of usable PSs or the first group ofunusable PSs. However, this is not necessarily so, and some of the PSsmay be unassigned for some frames, or may be assigned to anotherplurality (e.g., a plurality of PSs whose usability will be determinedbased on parameters other than the FET of the respective first frame,such as based on collected data). Optionally, the identifying of stage2404 may include determining which PSs qualify for one of the firstpluralities of PSs, and automatically regarding the rest of the PSs ofthe PDA (or of a predetermined subgroup of it, such as ROI) as belongingto the other plurality of PSs of the two.

It should be noted that the identifying of stage 2404 (and of stages2412 and 2402) does not have to reflect an actual usability states ofthe respective PSs (also in some implementations is does reflect theseactual usability states). For example, a PS which was included in thefirst group of unusable PSs may in fact be usable in the conditions ofthe first frame, while another PS which was included in the first groupof usable PSs may in fact be unusable in the conditions of the firstframe. The identifying of stage 2404 is an estimation or assessment ofthe usability of PSs of the PDA, and not a testing of the respectivePSs. It is also noted that usability of PSs may also be estimated instage 2404 based on other factors. For example, a preexisting list ofdefective PSs may be used to exclude such PSs from being consideredusable.

The identifying of stage 2404 (and of stages 2412 and 2420) may includeidentifying of at least one out of the groups of unusable PSs (and/or atleast one out of the groups of usable PSs) based on compound FET thatincludes a sum of durations during which sampling PSs of the PDD aresensitive to light and which excludes intermediate times between thedurations during which the sampling PSs are not sensitive to light.

The identifying of groups of usable and unusable PSs (in stages 2404,2412 and/or 2420) may be partly based on an assessment of temperature.Optionally, method 2400 may include processing one or more frames(especially previous frames or the present frame) for determining atemperature assessment (e.g., by assessing dark current level in a darkframe, or in darkened PSs which do not image the FOV). Method 2400 maythan include using the temperature assessment for identifying a group ofusable PSs and a group of unusable PSs for a later frame, which affectsthe generating of the respective image. The assessment of temperaturemay be used in assessing how quickly will the dark current saturate thedynamic range of a given PS for the duration of the relevant FET.Optionally, the temperature assessment may be used as a parameter forutilizing a usability model of the PS (e.g., one which is generated inmethod 2500).

The timing of execution of stage 2404 with respect to the timing ofexecution of stage 2402 may vary. For example, stage 2404 may optionallybe executed before, concurrently, partly-concurrently, or after stage2402 is executed. Referring to the examples of the accompanyingdrawings, stage 2404 may optionally be carried out by processor 2304and/or by controller 2314. Examples of methods for executing of theidentifying of stage 2404 are discussed with respect to method 1100.

Stage 2406 includes generating a first image based on the first framedetection levels of the first group of usable PSs, disregarding firstframe detection levels of the first group of unusable PSs. Thegenerating of the first image may be implemented using any suitablemethod, and may optionally be based on additional information (e.g.,data received from an active illumination unit, if used, data fromadditional sensors such as humidity sensors). Referring to the examplesset forth with respect to the previous drawings, it is noted that stage2406 may optionally be implemented by processor 2304. It is noted thatthe generating may include different stages of processing the signals(e.g., weighting, denoising, correcting, digitalizing, capping,level-adjustments, and so on).

With respect to the first group of unusable PSs, it is noted that sincedetection data by those PSs is ignored in the generating of the firstimage, replacement values could be computed in any suitable way (ifrequired). Such replacement values may be computed, for example, basedon first frame detection levels of neighboring PSs, based on earlierdetection levels of earlier frames, either of the same PS (e.g., ifusable in a preceding frame) or of one or more neighboring PSs (e.g.,based on kinematic analysis of the scene). For example, a Wiener filter,local mean algorithms, non-local means algorithms, and so on may beused. Referring to the generating of images based on the PDA data,optionally the generating of any one or more of such images (e.g., thefirst image, the second image and the third image) may include computinga replacement value for at least one pixel associated with a PSidentified as unusable for the respective image based on detection levelof at least one other neighboring PS identified as usable for therespective image. In cases in which nonbinary usability assessment isused (and the identifying of stages 2404, 2412 and/or 2420 includesidentifying at least one PS as belonging to a third group of PSs ofpartial usability), detection signals of each such PS identified aspartly usable can be combined or averaged with detection signals ofneighboring PSs and/or with other readings of the same PSs in othertimes in which it was usable (or partly usable).

Optionally, the generating of the first image (as well as that of thesecond image and the third image, later) may also include disregardingoutputs of PSs which are determined as defective, inoperative orunusable for any other reason, or which are determined to have adefective, inoperative or unusable detection path. An example foradditional method for detecting defectivity of PSs and/or associateddetection paths is discussed with respect to method 2200, which may becombined with method 2400. The outputs of method 2200 may be used forthe generating of stage 2406, 2414, and 2422. In such a case, method2200 may be executed periodically and provide outputs for the generatingof the images, or may be triggered specifically to be used in thegenerating of images according to method 2400.

Optionally, the generating of the first image (as well as that of thesecond image and the third image, later) may include computing areplacement value for at least one pixel associated with a PS identifiedas unusable for the respective image based on a detection level of thePS measured when the PS was identified as usable. Such information maybe used together with information of neighboring PSs or independentlyfrom it. Using detection levels of a PS from other times may include,for example: taking into account detection levels from previous frames(e.g., for stationary scenes), using detection information from anothersnap of a series of image acquisitions used in generation of a compoundimage such as a High-dynamic-range image (HDRI) or a multiple-wavelengthcompound image (in which several shots are taken using differentspectral filters and are then combined to a single image).

It is noted that in the first image (as well as in any other framesgenerated based on detection data of the PDA), a single pixel may bebased on the detection data from a single PS or from a combination ofPSs; likewise, the information from a single PSs may be used fordetermining pixel color of one or more pixels on the image. For example,a field of view of Θ by Φ degrees may be covered by X by Y PSs, and maybe translated to M by N pixels in the image. Φ pixel value for one ofthose M×N pixels may be calculated as a sum ofPixel-Value(i,j)=Σ(a_(p,s)·DL_(p,s)) for one or more PSs, where DL_(p,s)is the detection level of PS (p,s) for that frame, and a_(p,s) is anaveraging coefficients for the specific pixel (i,j).

Following stage 2406, the first image may than be provided to anexternal system (e.g., a screen monitor, a memory unit, a communicationsystem, an image processing computer). The first image may than beprocessed using one or more image processing algorithm. Following stage2406, the first image may then be otherwise handled as desired.

Stages 2402 through 2406 may be reiterated several times for many framescaptured by the photodetector sensor, whether consecutive frames or not.It is noted that in some implementations, the first image may begenerated based on detection levels of several frames, e.g., ifHigh-dynamic-range (HDR) imaging techniques are implemented. In otherimplementations, the first image is generated by on first framedetection levels of a single frame. Multiple instances of stages 2402and 2406 may follow a single instance of stage 2404 (e.g., if using thesame FET for several frames).

Stage 2408 is executed after receiving the first frame information, andincludes determining a second FET which is longer than the first FET.The determining of the second FET includes determining a duration forthe exposure of the relevant PDs (e.g., in milliseconds, parts thereofor multiples thereof). Stage 2408 may also include determiningadditional timing parameters (e.g., a start time for the exposure), butthis is not necessarily so. The second FET, which is longer with respectto the first FET, may be chosen for any reason. Such a reason mayinclude, for example, any one or more of the following: overall lightintensity in the FOV, light intensity in parts of the FOV, employingbracketing techniques, employing high dynamic range photographytechniques, changes in aperture, and so on. The second FET may be longerthan the first FET by any ratio, whether relatively low (e.g., ×1.1times, ×1.5 times), several times over (e.g., ×2, ×5) or any highervalue (e.g., ×20, ×100, ×5,000). Referring to the examples of theaccompanying drawings, stage 2408 may optionally be carried out bycontroller 2314 and/or by processor 2304. Optionally, an external systemmay determine the first FET or influence the setting of the FET by EOsystem 2300 (e.g., a control system of a vehicle in which EO system 2300is installed).

It is noted that optionally, at least one of stage 2408 and stage 2416may be replaced by do-determining together with such an external entitya new FET (the second FET and/or the third FET, respectively). Such anexternal entity may be, for example, an external controller, an externalprocessor, an external system. It is noted that optionally, at least oneof stage 2408 and stage 2416 may be replaced by receiving from anexternal entity an indication of a new FET (the second FET and/or thethird FET, respectively). The indication of the FET may be explicit(e.g., duration in milliseconds) or implicit (e.g., indication ofchanges in aperture opening and/or exposure value (EV), indication ofchanges in lightning duration which correspond to the FET). It is notedthat optionally, at least one of stage 2408 and stage 2416 may bereplaced by receiving from an external entity an indication of changesto expected dark current (or at least of the part of the dark currentwhich are transmitted to the capacitance of the PSs, e.g., if darkcurrent mitigation strategies are implemented).

Stage 2410 includes receiving second frame information. The second frameinformation includes for each of the plurality of PSs of the PDA asecond frame detection level which is indicative of an intensity oflight detected by the respective PS during the second FET. It is notedthat the second frame (during which the detection data for the secondframe information is collected) may directly follow the first frame, butthis is not necessarily so. FETs of any of the one or more intermediateframes (if any) between the first frame and the second frame may beequal to the first FET, the second FET, or any other FET (longer orshorter). Referring to the examples of the accompanying drawings, stage2410 may optionally be carried out by processor 2304 (e.g., via readoutcircuitry 2318).

Stage 2412 includes identifying out of the plurality of PSs of the PDD,based on the second FET, at least two types of PSs of the PDA:

a. A group of usable PSs for the second frame (referred to as “secondgroup of usable PSs”), that includes the first PS.b. A group of unusable PSs for the second frame (referred to as “asecond group of unusable PSs”) that includes the second PS, the thirdPS, and the fourth PS.

That is, the second PS and the third PSs which were identified in stage2404 as belonging to the first group of usable PSs (i.e., theaforementioned group of usable PSs for the first frame), are identifiedin stage 2412 as belonging to the second group of unusable PSs (i.e.,the aforementioned group of unusable PSs for the second frame), due tothe longer FET for the second frame. The identifying of stage 2412 maybe implemented in different ways, such as any one or more of thosediscussed above with respect to stage 2404. PSs which were considered asusable for shorter FET may be considered unusable in stage 2412 for thelonger FET for various reasons. For example, if such PSs have chargestorage capability (e.g., capacitance) which is lower than an averagecharge storage capability of PSs in the PDA, the charge storagecapability of those PSs may be considered insufficient for both thedetection signal and the accumulated dark current over longerintegration time. Any PS which is rendered unusable in the first FET dueto its inability to maintain sufficient dynamic range would also beidentified as unusable for the longer second FET, if the dark currentlevel is maintained (e.g., the temperature and bias on the PD areunchanged).

Stage 2412 is executed after stage 2408 (as it is based on the outputsof stage 2408). The timing of execution of stage 2412 with respect tothe timing of execution of stage 2410 may vary. For example, stage 2412may optionally be executed before, concurrently, partly-concurrently, orafter stage 2410 is executed. Referring to the examples of theaccompanying drawings, stage 2412 may optionally be carried out byprocessor 2304. Examples of methods for executing of the identifying ofstage 2412 are discussed with respect to method 2500.

Stage 2414 includes generating a second image based on the second framedetection levels of the second group of usable PSs, disregarding secondframe detection levels of the second group of unusable PSs.Significantly, stage 2414 includes generating the second image whileignoring the outputs (detection levels) of at least two PSs whoseoutputs were used in the generating of the first image. These at leasttwo PSs are identified as usable based on the FET of the first frame,and are identified as usable for the generating of the first image(i.e., at least the second PS and the third PSs). The generating of thesecond image may be implemented using any suitable method, including anymethod, technique and variations discussed above with respect to thegenerating of the first image. With respect to the second group ofunusable PSs, it is noted that since detection data by those PSs isignored in the generating of the second image, replacement values couldbe computed in any suitable way (if required). Following stage 2414, thesecond image may than be provided to an external system (e.g., a screenmonitor, a memory unit, a communication system, an image processingcomputer), may than be processed using one or more image processingalgorithm, or may then be otherwise handled as desired.

Stages 2410 through 2414 may be reiterated several times for many framescaptured by the photodetector sensor, whether consecutive frames or not.It is noted that in some implementations, the second image may begenerated based on detection levels of several frames, e.g., ifHigh-dynamic-range (HDR) imaging techniques are implemented. In otherimplementations, the second image is generated by on second framedetection levels of a single frame. Multiple instances of stages 2410and 2414 may follow a single instance of stage 2412 (e.g., if using thesame second FET for several frames).

Stage 2416 is executed after receiving the second frame information, andincludes determining a third FET which is longer than the first FET andshorter than the second FET. The determining of the third FET includesdetermining a duration for the exposure of the relevant PDs (e.g., inmilliseconds, parts thereof or multiples thereof). Stage 2416 may alsoinclude determining additional timing parameters (e.g., a start time forthe exposure), but this is not necessarily so. The third FET may bechosen for any reason, such as the ones discussed above with respect tothe determining of the second FET in stage 2408. The third FET may belonger than the first FET by any ratio, whether relatively low (e.g.,×1.1 times, ×1.5 times), several times over (e.g., ×2, ×5) or any highervalue (e.g., ×20, ×100, ×5,000). The third FET may be shorter than thesecond FET by any ratio, whether relatively low (e.g., ×1.1 times, ×1.5times), several times over (e.g., ×2, ×5) or any higher value (e.g.,×20, ×100, ×5,000). Referring to the examples of the accompanyingdrawings, stage 2416 may optionally be carried out by controller 2314and/or by processor 2304. Optionally, an external system may determinethe first FET or influence the setting of the FET by EO system 2300.

Stage 2420 of method 2400 includes receiving third frame information.The third frame information includes for each of the plurality of PSs ofthe PDA a third frame detection level which is indicative of anintensity of light detected by the respective PS during the third FET.It is noted that the third frame (during which the detection data forthe third frame information is collected) may directly follow the secondframe, but this is not necessarily so. FETs of any of the one or moreintermediate frames (if any) between the second frame and the thirdframe may be equal to the second FET, the third FET, or any other FET(longer or shorter). Referring to the examples of the accompanyingdrawings, stage 2420 may optionally be carried out by processor 2304(e.g., via readout circuitry 2318).

Stage 2420 includes identifying out of the plurality of PSs of the PDD,based on the third FET, at least two types of PSs of the PDA:

a. A group of usable PSs for the third frame (referred to as “thirdgroup of usable PSs”) that includes the first PS and the second PS.b. A group of unusable PSs for the third frame (referred to as “a thirdgroup of unusable PSs”) that includes the third PS and the fourth PS.

That is, the second PS which was identified in stage 2404 as belongingto the first group of usable PSs (i.e., the aforementioned group ofusable PSs for the first frame) is identified in stage 2420 as belongingto the third group of unusable PSs (i.e., the aforementioned group ofunusable PSs for the third frame), due to the longer FET for the thirdframe with respect to the first frame. The third PS which was identifiedin stage 2412 as belonging to the second group of unusable PSs (i.e.,the aforementioned group of unusable PSs for the second frame) isidentified in stage 2420 as belonging to the third group of usable PSs(i.e., the aforementioned group of usable PSs for the third frame), dueto the shorter FET for the third frame with respect to the second frame.

The identifying of stage 2420 may be implemented in different ways, suchas any one or more of those discussed above with respect to stage 2404.PSs which were considered as usable for shorter FET may be consideredunusable in stage 2420 for the longer FET for various reasons, e.g., asdiscussed above with respect to stage 2412. PSs which were considered asunusable for longer FET may be considered usable in stage 2420 for theshorter FET for various reasons. For example, if such PSs have chargestorage capability (e.g., capacitance) which is larger than that of someof the PSs in the second group of unusable PSs, the charge storagecapability of those differing PSs may be considered sufficient for boththe detection signal and the accumulated dark current over a shorterintegration time than the second FET.

Stage 2420 is executed after stage 2416 (as it is based on the outputsof stage 2416). The timing of execution of stage 2420 with respect tothe timing of execution of stage 2416 may vary. For example, stage 2420may optionally be executed before, concurrently, partly-concurrently, orafter stage 2416 is executed. Referring to the examples of theaccompanying drawings, stage 2420 may optionally be carried out byprocessor 2304 and/or by controller 2314. Examples of methods forexecuting of the identifying of stage 2420 are discussed with respect tomethod 1100.

Stage 2422 includes generating a third image based on the third framedetection levels of the third group of usable PSs, disregarding thirdframe detection levels of the third group of unusable PSs.Significantly, stage 2422 includes generating the third image whileignoring the outputs (detection levels) of at least one PS whose outputswere used in the generating of the first image (e.g., the second PS)while utilizing the outputs of at least one PS whose outputs wereignored in the generating of the second image (e.g., the third PS). Thegenerating of the third image may be implemented using any suitablemethod, including any method, technique and variations discussed abovewith respect to the generating of the first image. With respect to thethird group of unusable PSs, it is noted that since detection data bythose PSs is ignored in the generating of the third image, replacementvalues could be computed in any suitable way (if required). Followingstage 2422, the third image may than be provided to an external system(e.g., a screen monitor, a memory unit, a communication system, an imageprocessing computer). Following stage 2422, the third image may than beprocessed using one or more image processing algorithm. Following stage2422, the third image may then be otherwise handled as desired.

Optionally, the generating of one or more images in method 2400 (e.g.,the first image, the second image, the third image) may be based on aprevious stage of assessing dark current accumulation of at least one ofthe PSs for the respective image (e.g., based at least on the respectiveFET, on electrical measurement during the capturing of the light signalor close thereto, and so on. For example, such measurement may includemeasuring dark current (or another indicative measurement) on areference PS kept in the dark. The generating of the respective imagemay include subtracting from the detection signal of one or more PSs amagnitude which is related to the dark current assessment for that PS,to give a more accurate representation of the FOV of the PDA.Optionally, this stage of compensating for dark current accumulation iscarried out only for usable PSs for the respective image.

In a PDA which is characterized by relatively high dark current (e.g.,as a result of the type and characteristics of its PDs), the capacitanceof the individual PSs in which detection charge is collected may becomesaturated (partly or fully) by the dark current, leaving little to nodynamic range for detection of ambient light (arriving from a field ofview of the system). Even when means for subtracting dark current levelsfrom the detection signals are implemented (e.g., to normalize thedetection data), the lack of dynamic range for detection means that theresulting signal is completely saturated, or insufficient for meaningfuldetection of ambient light levels. Since dark current from the PD isaccumulated in the capacitance (whether actual capacitor or parasitic orresidual capacitance of other components of the PSs) for the FET, themethod uses the FET for determining that the PS is usable for therespective FET—is there sufficient dynamic range left in the capacitanceafter the charge of the dark current (or at least relevant part thereof)is collected for the entire FET. The identifying of a group of unusablePSs for a frame may include identifying PSs whose dynamic range is belowan acceptable threshold (or is otherwise expected to fail a dynamicrange sufficiency criterion) given the FET of the respective frame.Likewise, the identifying of a group of usable PSs for a frame mayinclude identifying PSs whose dynamic range is above an acceptablethreshold (or is otherwise expected to meet a dynamic range sufficiencycriterion) given the FET of the respective frame. The two aforementionedthresholds of acceptability may be the same threshold or differentthreshold (for example, if PSs whose dynamic range are between thosethresholds are treated differently, e.g., are identified as belonging toa partly usable group of PSs for the relevant frame).

Referring to method 2400 as a whole, it is noted that additionalinstances of stages 2416, 2418, 2420 and 2422 may be repeated foradditional FETs (e.g., a fourth FET and so on). Such time may be longer,shorter, or equal to any of the previously used FETs. It is also notedthat optionally, the first FET, the second FET, and the third FET areconsecutive FETs (i.e., not other FETs are used by the PDA between thefirst FET and the third FET). Alternatively, other FETs may be usedbetween the first FET and the third FET.

It is noted that different groups of usable PSs and unusable PSs may bedetermined for different FETs in method 2400, even if the exposure value(EV) remains the same. For example, consider a case in which the firstFET is extended by a factor q to provide the second FET, but the fnumber is increased by a factor of q, such that the overall illuminationreceived by the PDA is substantially the same. In such a case, eventhough the EV remains constant, the second group of unusable PSs wouldinclude PS other than those included in the first group of unusable PSs,because the dark current accumulation will grow by a factor of q.

A non-transitory computer-readable medium is provided for generatingimage information based on data of a PDA, including instructions storedthereon, that when executed on a processor, perform the steps of:receiving first frame information comprising for each out of a pluralityof PSs of the PDA a first frame detection level indicative of anintensity of light detected by the respective PS during a first FET;based on the first FET, identifying out of the plurality of PSs of thePDD: a first group of usable PSs comprising a first PS, a second PS, anda third PS, and a first group of unusable PSs comprising a fourth PS;generating a first image based on the first frame detection levels ofthe first group of usable PSs, disregarding first frame detection levelsof the first group of unusable PSs; (d) determining, after receiving thefirst frame information, a second FET which is longer than the firstFET; receiving second frame information comprising for each of theplurality of PSs of the PDA a second frame detection level indicative ofan intensity of light detected by the respective PS during a second FET;based on the second FET, identifying out of the plurality of PSs of thePDD: a second group of usable PSs comprising the first PS, and a secondgroup of unusable PSs comprising the second PS, and the third PS, andthe fourth PS; generating a second image based on the second framedetection levels of the second group of usable PSs, disregarding secondframe detection levels of the second group of unusable PSs; determining,after receiving the second frame information, a third FET which islonger than the first FET and shorter than the second FET; receivingthird frame information comprising for each of the plurality of PSs ofthe PDA a third frame detection level indicative of an intensity oflight detected by the respective PS during a third FET; based on thethird FET, identifying out of the plurality of PSs of the PDD: a thirdgroup of usable PSs comprising the first PS and the second PS, and athird group of unusable PSs comprising the third PS and the fourth PS;and generating a third image based on the third frame detection levelsof the third group of usable PSs, disregarding third frame detectionlevels of the third group of unusable PSs.

The non-transitory computer-readable medium of the previous paragraphmay include additional instructions stored thereon, that when executedon a processor, perform any other step or variation discussed above withrespect to method 2400.

FIG. 25 is a flow chart illustrating method 2500 for generating a modelfor PDA operation in different FETs, in accordance with examples of thepresently disclosed subject matter. Identifying which of the PSs belongto a group of usable PSs provided with a given FET (and possiblyadditional parameters, such as temperature, biases on PDs, PSscapacitance, etc.) may be based on a model of the behavior of each ofthe PSs at different FETs. Such modeling may be part of method 2400 ormay be executed separately before it. Stages 2502, 2504 and 2506 ofmethod 2500 are executed for each out of a plurality of PSs of the PDA(e.g., PDA 1 602), and possibly for all of the PSs of the photodetectorarray.

Stage 2502 includes determining the usability of the respective PS foreach FET out of a plurality of different FETs. The determining of theusability may be executed in different ways. For example, a detectionsignal of the PS may be compared to an expected value (e.g., ifillumination level is known—possibly completely dark, or a known higherillumination level), to an average of other PSs, to detection levels inother PSs (e.g., if all PSs are imaging a chromatically uniform target),to detection results in other FETs (e.g., determining if the detectionlevel at duration T—for example, 200 nanoseconds—is about double thedetection level at T/2—in that example, 330 nanoseconds), and so on. Thedetermined usability may be a binary value (e.g., usable or unusable), anon-binary value (e.g., a scalar assessing level of usability orindicative thereof), a set of values (e.g., a vector), or any othersuitable format. Optionally, the same plurality of frame FETs is usedfor all of the plurality of PSs, but this is not necessarily so. Forexample, in a non-binary usability assessment, an intermediate valuebetween completely unusable to fully usable may indicate that thedetection signal of the respective PS should be combined or averagedwith detection signals of neighboring PSs and/or with other readings ofthe same PSs in other times in which it was usable (or partly usable).

Method 2500 may include an optional stage 2504 of measuring the chargeaccumulation capacity and/or saturation parameters for the respectivePS. The charge capacity may be measured in any suitable way, e.g., usingcurrent coming from the PD, from other source in the PS (e.g., currentsource), from other source in the PDA, or from an external source (e.g.,calibration machine in the manufacturing facility in which thephotodetector is manufactured). Stage 2504 may be omitted, for example,in case the difference is capacitance between the different PSs arenegligible or simply ignored.

Stage 2506 includes creating a usability prediction model for therespective PS, which provides estimation of usability of the PS whenoperated under different FET which are not included in the plurality ofFETs for which the usability was actively determined in stage 2502. Thedifferent FETs may be included in the same span of durations of theplurality of FETs of stage 2502, longer from it, or shorter from it. Thecreated usability prediction model may provide different types ofusability indications, such as: a binary value (e.g., usable orunusable), a nonbinary value (e.g., a scalar assessing level ofusability or indicative thereof), a set of values (e.g., a vector), orany other suitable format. The usability type indicated by the model maybe the same type of usability determined in stage 2502 or differentthereof. For example, stage 2502 may include assessing the dark currentcollected in different FETs, while stage 2504 may include determining atemporal threshold which indicates the maximal permissible FET for thisPS to be considered usable. Optionally, the usability model may takeinto account the charge accumulation capacity of the respective PS.

Any suitable way may be used for creating the usability predictionmodel. For example, different dark currents may be measured or assessedfor the PD for different FETs, followed by a regression analysis todetermine a function (polynomial, exponential, etc.) which allowassessing the dark current in other FETs.

Optional stage 2508 includes compiling a usability model for at least aportion of the PDA, including at least the plurality of PSs of theprevious stages. For example, stage 2508 may include generating one ormore matrixes or other types of maps which store model parameters in itscells for the respective PSs. For example, if stage 2506 includescreating a dark current linear regression function for each PS (p,s) isprovided by DarkCurrent(p,s)=A_(p,s)·Σ+B_(p,s) (where τ is the FET andA_(p,s) and B_(p,s) are the linear coefficients of the linearregression), than a matrix A may be generated for storing the differentA_(p,s) values, and a matrix B may be generated for storing thedifferent B_(p,s) values. If needed, a third matrix C may be used forstoring a different capacitance values C_(p,s) (or different saturationvalues S_(p,s)) for the different PSs.

Stage 2506 (or stage 2508, if implemented) may be followed by optionalstage 2510 that includes determining the usability of the plurality ofPSs for a FET which is not one of the plurality of FETs of stage 2502based on the results of stage 2506 (or of stage 2508, if implemented).For example, stage 2510 may include creating a mask (e.g., a matrix) ofunusable PSs for the different PSs of the photodetector array.

Referring to method 2500 in its entirety, stage 2502 may includedetermining the dark current for each PS of the PDA at four differentFETs (e.g., 33 ns, 330 ns, 600 ns, and 2000 ns). Stage 2504 may includedetermining a saturation value for each of the PSs, and stage 2506 mayinclude creating a polynomial regression for dark current accumulationover time for each of the PSs. Stage 2508 in this example may includegenerating a matrix, storing in each cell the FET in which the darkcurrent of that PS (according to the regression analysis) will saturatethe PS. Stage 2510 may include receiving a new FET, and determining foreach cell of the matrix if it is lower or higher than the stored value,following by generating a binary matrix storing a first value (e.g.,“0”) for each unusable PS (in which the FET is higher than the storedvalue) and a second value (e.g., “1”) for each usable PS (in which theFET is lower than the stored value).

Any stage of method 2500 may be carried out during manufacturing of thePDA (e.g., during factory calibration), during operation of the system(e.g., after an EO system which includes the PDA is installed in itsdesignated location such as a vehicle, surveillance system, etc.), or inany other suitable time between or after those times. Different stagesmay be carried out in different times.

Referring to method 2400 in its entirety, it is noted that the differentstages may be extended to measure effects of dark current on thedifferent PSs in different FETs under different operational conditions(e.g., when different subject to different temperatures, when differentbiases are applied to the PDs), mutatis mutandis.

Optionally, the determining of a FET as part of method 2400 (e.g., thesecond FET, the third FET) may include maximizing the respective FETwhile maintaining a number of unusable PSs for the respective framebelow a predetermined threshold. For example, to maximize collection ofsignals, method 2400 may include setting a FET which is approaching athreshold which correlates to a predetermined number of unusable PSs(e.g., requiring at least 99% of the PDA PSs to be usable, permitting upto 1% of the PSs to be unusable). It is noted that is some cases themaximizing may not yield the exact maximal duration, but a durationwhich is close to it (e.g., above 320% or above 325% of themathematically maximal duration). For example, the maximal frameduration out of discrete predefined time spans may be selected.

For example, a determining of a FET as part of method 2400 may includedetermining a FET which is longer than other possible FETs, therebycausing more PSs than a previous FET, thereby causing a higher number ofPSs deemed unusable in comparison to such other possible FETs, butimproving the image quality in the remaining PSs. This may be useful,for example, in relatively dark conditions. It is noted that optionally,the determining of the FET (e.g., by way of attempting to maximize it)may take into consideration the spatial distribution of PSs which areconsidered unusable in different FETs. For example, knowing that in somearea of the PDA there is an accumulation of PSs with high percentage ofPSs which will be deemed unusable above a certain FET may causedetermining a FET which is lower than that threshold, especially if thisan important part of the FOV (e.g., in a center of the FOV, or wherepedestrians or vehicles were identified in a previous frame).

Method 2400 may include creating a single image based on detectionlevels of two or more frames which are detected at different FETs, inwhich different groups of unusable PSs are used for the different FETs.For example, three FETs may be used: ×1, ×10, and ×100. The colordetermined for each pixel of the image may be determined based on thedetection levels of one or more PSs (e.g., at FETs in which the PS isusable, not saturated, and detecting a nonnegligible signal) or ondetection levels of neighboring PSs (e.g., if not providing any usabledetection signal, even in cases in which the respective PS is determinedto be usable, such as because in such times the signal is negligible).Method 2400 may include determining a plurality of FETs for combiningdifferent exposures to a single image (e.g., using High-Dynamic-Rangeimaging techniques—HDR). The determining of such FETs may be based onmodeling of the usability of different PSs in different FETs such as themodel generated in method 2500. Method 2400 may also include determiningto capture a single image in two or more distinct detection instances(where the detection signals are read separately in each instance andare later summed), each of which providing sufficient usable PSs. Forexample, instead of taking a single capture of a scene using 2milliseconds FET, method 2400 may include determining to capture thescene twice (e.g., two 1 ms FETs, a 1.5 ms and a 0.5 ms FETs), such thatthe number of usable PSs in each exposure would exceed a predeterminedthreshold.

Optionally, method 2400 may include determining at least one of the FETsbased on a usability model of the different PSs in different FETs (e.g.,generated in method 2500) and on saturation data of at least oneprevious frame captured by the PDA. The saturation data includesinformation about PSs which were saturated in at least one FET of atleast one previous frame (e.g., number of PSs, which PSs, which parts ofthe PDA) and/or about which PSs were almost saturated in at least oneFET of at least one previous frame. The saturation data may pertain tothe immediately preceded frame (or several frame), so it is indicativeon saturation behavior for a curtain imaged scene.

Method 2400 may further include modeling usability of PSs of the PDA atdifferent FETs (e.g., by implementing method 2500 or any other suitablemodeling method). Provided a model of usability of PSs of the PDA atdifferent FETs (either as part of method 2400 or not), method 2400 mayinclude: (a) determining of at least one FET out of the second FET andthe third FET based on results of the modeling; and/or (b) identifyingof at least one out of the groups of unusable PSs based on results ofthe modeling.

Optionally, in determining any one or more of the FETs, method 2400 mayinclude determining a FET which balances between extending the FET dueto darkness of the FOV scene and reducing of the FET to limit the amountof PSs rendered unusable which rises in longer FET (e.g., based on themodel of method 2500). For example, when working in the same temperatureand bias on the PD (such that the dark current in each FET remainsconstant), stage 2408 may include determining a longer FET because thescene got darker (at the expense of a larger number of unusable PSs),and stage 2416 may include determining a shorter FET because the scenegot brighter again (thereby reducing the number of unusable PSs). Thisis especially relevant in darker images, where usability of PSsresulting from dark current accumulation (which result from temperatureand operational conditions but not from illumination level) limits theelongating of the FET which would be carried out if dark currentaccumulation would not significantly limit the dynamic range of therespective PSs. In another example, within a time span in which thescene lighting remains constant, stage 2408 may include determining alonger FET enabled by temperature fall (thereby lowering the darkcurrent and with it the percentage of unusable PSs at each FET), whilestage 2416 may include determining a shorter FET because the temperatureof the PDA rose again.

FIG. 26 is a graphical representation of execution of method 2400 forthree frames which are taken of the same scene in different FETs, inaccordance with examples of the presently disclosed subject matter. Theexample scene includes including four concentric rectangles, each darkerfrom the one surrounding it. Different diagrams of FIG. 26 correspond toa stage of method 2400, and are numbered with an equivalent referencenumber with an apostrophe. For example, diagram 2406′ matches anexecution of stage 2406, and so on. Each rectangle in the lower ninediagrams represents a single PS, or a pixel which maps directly ontosuch PS (in the lower three diagrams). In all of the diagrams, thelocation of the PSs with respect to the PDD remains constant.

As common in many types of PDAs, the PDA from which frame information isreceived may include bad, defective, or otherwise misbehaving PSs (alsoreferred to as bad, defective, or otherwise misbehaving pixels). Theterm “Misbehaving PS” broadly pertains to a PS deviating from itsexpected response, encompassing but not limited to stuck, dead, hot,lit, warm, defective, and flashing PSs. Misbehaving PSs may beindividual PSs or clusters of PSs. Non-limiting examples of defectswhich may cause a PS to misbehave include: PS bump bond connectivity,addressing faults in the multiplexer, vignetting, severe sensitivitydeficiency of some PSs, non-linearity, poor signal linearity, low fullwell, poor mean-variance linearity, excessive noise and high darkcurrent. One or more of the PSs which are identified as an unusable PSin method 2400 may be a permanently misbehaving PS, or such which ismisbehaving based on conditions which are unrelated to FET (e.g., due tohigh temperature). Such PSs may be identified as unusable for all of theFETs of method 2400 (e.g., PS 8012.5). It is nevertheless noted thatsome functional PSs (which are not “misbehaving”) may be consideredunusable in all of the FETs of method 2400 because of limited capacityand sufficiently long FETs (e.g., PS 8012.4). Optionally, method 2400may include determining usability of one or more of the PSs of the PDAbased on other parameters in addition to FET (e.g., temperature,electric parameters, ambient light level). It is noted that in suchcases, a PS which would be rendered unusable for reasons of FET cannotusually be nevertheless considered usable due to other considerations(such as temperature), because of its capacitance limitation.

In the illustrated example:

a. PS 8012.5 outputs no signal regardless of the amount of lightimpinging on it in all three FETs (T₁,T₂,T₃); possibly under allconditions.b. PS 8012.4 outputs saturated signal regardless of the amount of lightimpinging on it in all three FETs (T₁,T₂,T₃); possibly under allconditions.c. PS 8012.3 outputs a usable signal at the shortest FET, T₁, but anon-usable (saturated) signal at the longer FETs T₂ and T₃.d. PS 8012.2 outputs a usable signal at the shorter FETs T₁ and T₃, buta non-usable (saturated) signal at the longest FET, T₂.

It is noted that other types of defects and of erroneous outputs mayalso occur. Such errors may include, by way of example: outputting ahighly non-linear signal response, consistently outputting too strong asignal, consistently outputting too week a signal, outputting random orsemi-random output, and so on. Also, many PSs (such as first PS 8012.1)may be usable in all FETs used in the detection.

Reverting to FIG. 23, it is noted that optionally system 2300 may be anEO system which have dynamic PS usability assessment capabilities. Thatis, EO system 2300 may be able to alternately assign different PSs asusable or unusable, based on FET and possibly other operationalparameters, and to utilize the detection signals of PSs only whendetermined that the respective PSs were usable at the time of capturing(e.g., according to a usability model).

In such a case, EO system 2300 includes:

-   -   a. PDA 2302, which includes a plurality of PSs 2306, each        operative to output detection signals at different frames. The        detection signal output for a frame by the respective PS 2306        being indicative of amount of light impinging on the respective        PS during a respective frame (and possibly also on dark current        of the PD of the respective PS).    -   b. A usability filtering module (e.g., implemented as part of        processor 2304, or separately thereof). The usability filtering        module is operative to determine for each PSs 2306 that the PS        is unusable based on a first FET (which may be different between        different PSs 2306), and to later determine that the same PS        2306 is usable based on a second FET that is shorter than the        first FET. That is, PSs 2306 which were unusable at one point        (and whose output was ignored in the generating of one or more        images) may later become usable again (e.g., if the FET gets        shorter) and the outputs of those PSs 2306 can be useful again        in the generation of following images.    -   c. Processor 2304 which is operative to generate images based on        frame detection levels of the plurality of PSs 2306. Among other        configurations of the processor 2304, it is configured to: (a)        exclude, when generating a first image based on first frame        detection levels, a first detection signal of a filtered PS that        was determined by the usability filtering module as unusable for        the first image, and (b) include, when generating a second image        based on second frame detection levels captured by the PDA after        the capturing of the first frame detection levels, a second        detection signal of the filtered PS that was determined by the        usability filtering module as usable for the second image.

Optionally, controller 2314 may determine different FETs for differentframes, based on differing illumination levels of objects in the fieldof view of the EO system.

Optionally, controller 2314 may be configured to determine FETs for theEO system by maximizing FETs while maintaining a number of unusable PSsfor the respective frames below a predetermined threshold (e.g., asdiscussed with respect to method 2400).

Optionally, EO system 2300 may include comprising at least one shieldedPD which is shielded from ambient illumination (e.g., by a physicalbarrier, or using deflecting optics), as well as dedicated circuitrywhich is operative to output electric parameter indicative of level ofdark current based on signal level of the at least one shielded PD.Processor 2304 may be configured to generate images based on theelectric parameter, on the respective FET, and on the detection signalsof the PDA, thereby compensating for differing degrees of dark currentaccumulation in different frames.

Optionally, processor 2304 may be operative to compute a replacementvalue for at least one pixel of the first image that is associated withthe filtered PS, based on a detection level of the filtered PS measuredwhen the PS was identified as usable. Optionally, processor 2304 may beconfigured to compute replacement values for PSs when detection signalsby the respective PSs are excluded from the generating of images, basedon detection level of neighboring PSs. Optionally, processor 2304 may beoperative to compute a replacement value for at least one pixel of thefirst image that is associated with the filtered PS, based on a firstframes detection levels neighboring PSs.

Optionally, processor 2304 (or usability filter module, if not part ofthe processor) may be operative to determine a degree of usability forPSs based on a FET, the degree including a sum of durations during whichsampling PSs of the PDD are sensitive to light and which excludesintermediate times between the durations during which the sampling PSsare not sensitive to light.

Optionally, processor 2304 may utilize a usability model generatedaccording to method 2500 to determine when to include and when toexclude detection signals of different PSs, captured at different FETs.Optionally, EO system 2300 may be operative to execute method 2500.Optionally, EO system 2300 may be configured to participate in executionof method 2500 together with an external system (such as a factorycalibration machine used in the manufacturing of EO system 2300).

FIG. 27 is a flow chart illustrating an example of method 3500, inaccordance with the presently disclosed subject matter. Method 3500 isused for generating images based on different subsets of PSs indifferent operational conditions. Referring to examples set forth withrespect to the previous drawings, method 3500 may be executed byprocessor 1 604, where the PDA of method 3500 may optionally be PDA 1602. Method 3500 includes at least stages 3510, 3520, 3530 and 3540,which are repeated as a sequence for different frames captured by aphotodetector array. The sequence may be executed in full for everyframe in a stream, but this is not necessarily so, as discussed below ingreater detail.

The sequence starts with stage 3510 of receiving from the PDA frameinformation indicative of detection signals for the frame which areprovided by a plurality of PSs of the PDA. The frame information mayinclude detection level (or levels) for each of the PSs (e.g., between 0and 1024, three RGB values, each between 0 and 255, and so on), or anyother formats. The frame information may be indicative of detectionsignals in indirect manners (e.g., information pertaining to thedetection level of a given PS may be given with respect to the level ofa neighboring PS or with respect to the level of the same PS in aprevious frame). The frame information may also include additionalinformation (e.g., serial number, timestamp, operational conditions),some of which may be used in following steps of method 3500. The PDAfrom which frame information is received may include bad, defective, orotherwise misbehaving PSs.

Stage 3520 includes receiving operational conditions data indicative ofoperational conditions of the PDA during the frame duration. Theoperational conditions may be received from different types of entities,such as any one or more of the following entities: the PDA, a controllerof the PDA, the at least one processor which executes method 3500, oneor more sensors, one or more controllers of the at least one processorwhich executes method 3500, and so on. Non-limiting examples ofoperational conditions which may be referred in stage 3520 include FETof the PDA (e.g., electronic or mechanical shutter, flash illuminationduration and so on), amplification gain of the PDA or connectedcircuitry, bias applied to PDs of the PDA, ambient light levels,dedicated illumination levels, image processing mode of downstream imageprocessor, filtering applied to the light (e.g., spectral filtering,polarization) and so on.

Stage 3530 includes determining—based on the operational conditionsdata—a group of defective PSs that includes at least one of the PSs andexclude a plurality of the other PSs. When stage 3530 is executed fordifferent frames based on different operational conditions data receivedfor these frames in different corresponding instances of stage 3520,different groups of defective PSs are selected for different frameswhose operational conditions are different for each other. However, thesame group of defective pixels may be selected for two frames withdifferent operational conditions (e.g., when the difference inoperational conditions relatively small).

It is noted that the determining is based on the operational conditionsdata and not on evaluating the PSs themselves, and therefore thedefectivity of the various PSs included in the different groups is anestimation of their condition, and not a statement about their actualoperability conditions. Thus, a PS which is included in the group ofdefective PSs in stage 3530 is not necessarily defective or inoperativein the operational conditions indicated in the operational conditionsdata. The determining of stage 3530 is intended to match as accuratelyas possible to the actual real-life state of the PDA.

Stage 3540 includes processing the frame information to provide an imagerepresenting the frame. The processing is based on detection signals ofPSs of the photodetector, excluding PSs included in the group ofdefective PSs. That is, the detections signals from the PSs of the PDAare used to generate an image representing the field of view (or otherscene, or one or more objects whose light reaches the PDA), but avoidingall detection signals originating in PSs which are included in the groupof defective PSs (which, as aforementioned, is dynamically determinedbased on the operational conditions data during the time in which therelevant frame information was captured). Stage 3540 may optionallyinclude computing replacement values to compensate for ignored detectionsignals. Such computing may include, for example, determining areplacement value for a defective PS, based on the detection signals ofneighboring PSs. Such computing may include, for example, determining areplacement value for a pixel of the image based on the values ofneighboring pixels of the image. Any technique discussed above withrespect to generating of images in method 2400 may also be used for thegenerating of images in stage 3540.

An example for execution of the method for two frames (a first frame anda second frame) may include, for example:

-   -   a. Receiving from the PDA first frame information indicative of        first detection signals provided by a plurality of PSs and        pertaining to a first frame duration, the plurality of PSs        including at least a first PS, a second PS, and a third PS. A        frame duration is the time during which light collected by the        PDA is aggregated to a single image or a frame of a video.        Different frame duration may be mutually exclusive, but in some        embodiment may optionally be partially overlapping.    -   b. Receiving first operational-conditions data, indicative of        operational conditions of the PDA during the first frame        duration.    -   c. Determining—based at least on the first operational        conditions data—a first group of defective PSs, including the        third PS and excluding the first PS and the second PS. The        determining may include directly determining the first group of        defective PSs, or determining other data which implies which        pixels are considered defective (e.g., determining a complement        set of non-defective pixels, assigning a defectivity level for        each pixel and later setting a threshold or other determining        criteria).    -   d. Processing, based on the first group of defective PSs, the        first frame information to provide a first image, such that the        processing is based at least on the first detection signals of        the first PS and the second PS (optionally following preceding        preprocessing, such as digitalization, capping,        level-adjustments, and so on), and ignores information        pertaining to detection signals of the third PS.    -   e. Receiving from the PDA second frame information indicative of        second detection signals provided by a plurality of detection        PSs. The second frame information pertains to a second frame        duration other than the first frame duration.    -   f. Receiving second operational conditions data, indicative of        operational conditions of the PDA during the second frame        duration, which are different than the first operational        conditions data. It is noted that the second        operational-conditions data may be received from the same source        from which the first operational-conditions data was received,        but this is not necessarily so.    -   g. Determining, based on the second operational conditions, data        a second group of defective PSs, including the second PS and the        third PS and excluding the first PS. The determining may include        directly determining the second group of defective PSs, or        determining other data which implies which pixels are considered        defective (e.g., determining a complement set of non-defective        pixels, assigning a defectivity level for each pixel and later        setting a threshold or other determining criteria).    -   h. Processing the second frame information based on the second        group of defective PSs to provide a second image, such that the        processing of the second image information is based at least on        the second detection signals of the first PS and ignores        information pertaining to detection signals of the and the        second PS and of the third PS.

FIG. 28A illustrates system 3600 and exemplary target objects 3902 and3904, in accordance with examples of the presently disclosed subjectmatter. EO system 3600 includes at least processor 3620 which isoperative to process detection signals from at least one PDA (which maybe part of the same system, but it not necessarily so) to generateimages representing objects in a field of view of system 3600. System3600 may be implemented by a system 2300, and similar reference numberare used (for example, in such a case PDA 3610 may be PDA 2302,controller 3640 may be controller 2314, and so on), but this is notnecessarily so. For reasons of brevity, not all of the descriptionprovided above with respect to system 2300 is repeated, and it is notedthat any combination of one or more components of system 2300 may beimplemented, mutatis mutandis, in system 3600, and vice versa. System3600 may be a processing system (e.g., a computer, a graphicalprocessing unit) or an EO system which further includes a PDA 3610 andoptics. In the latter case, system 3600 may be any type of EO systemwhich uses PDA for detection, such as a camera, a spectrograph, a LIDAR,and so on. Optionally, system 2600 may include one or more illuminationsources 3650 (e.g., lasers, LEDs) for illuminating objects in the FOV(e.g., for illuminating the object for at least the first FET and thesecond FET). Optionally, system 3600 may include controller 3640 whichis operative to determine different FETs for different frames, based ondiffering illumination levels of objects in the field of view of the EOsystem. Optionally, those different FETs may include the first FETand/or the second FET.

Two exemplary targets are illustrated in FIG. 28A: a dark color car 3902(having low reflectivity body panels) with a highly reflective licenseplate, and a black rectangular panel 3904 with a white patch on it. Itis noted that system 3600 is not necessarily limited to generatingimages of low reflectivity objects with high reflectivity patches.However, the way system 3600 generates images of such targets isinteresting.

Processor 3620 is configured to receive from a PDA (e.g., PDA 3610, ifimplemented) multiple detection results of an object that includes ahigh reflectivity surface surrounded by low reflectivity surfaces on allsides (exemplified by targets 3902 and 3904). The multiple detectionresults include: (a) first frame information of the object detected bythe PDA during a first FET, and (b) second frame information of theobject detected by the PDA during a second FET that is longer than thefirst FET. The first frame information and the second frame informationare indicative of detection signals output by different PSs of the PDAwhich are in turn indicative of light intensities of different parts ofthe target which are detected by the PDA. Some PSs detect light from lowreflectivity parts of the objects while at least one other PS detectslight from the high reflectivity surface.

Based on the different FETs, processor 3620 process the first frameinformation and the second frame information differently. FIG. 28Billustrates exemplary first image and the second image of targets 3902and 3904, in accordance examples of the presently disclosed subjectmatter. When processing the first frame information, processor 3620processes the first frame information, based on the first FET. Itgenerates a first image that includes a bright region representing thehigh reflectivity surface, surrounded by a dark background representingthe low reflectivity surfaces. This is illustrated in FIG. 28B as firstimages 3912 and 3914 (corresponding to objects 3902 and 3904 of FIG.28A). When processor 3620 processes the second frame information, basedon the second FET, which is longer than the first FET. Tt generates asecond image that includes a dark background without a bright region.This is illustrated in FIG. 28B as second images 3922 and 3924(corresponding to objects 3902 and 3904 of FIG. 28A).

That is, even though more light of the highly reflective surface reachesthe respective PSs of the photodetector at the second frame, the imageoutput is not lighter nor saturated, it is darker. Processor 3620 maydetermine the darker color for the pixels representing the highreflectivity surface in the second image by using information ofneighboring PSs (which have lower intensity signals, as they capturelower reflectivity surfaces of the object) because it determined thatthe signals from the relevant PSs are unusable in that longer secondFET. Optionally, processor 3620 may be configured to discard detectedlight signals corresponding to the high reflectivity surface whengenerating the second image based on the second FET (and optionally alsoon usability modeling of the respective PSs, e.g., as discussed withrespect to method 2500), and to compute a dark color for at least onecorresponding pixel of the second image in response to detected lightintensities from neighboring low reflectivity surfaces of the objectscaptured by neighboring PSs. Optionally, the decision by processor 3620to discard information of the respective PS is not based on thedetection signal level but rather on the susceptibility of therespective PS to dark current (e.g., limited capacitance). Optionally,when processing of the second frame information, processor 3620 mayidentify at least one PS which detects light from the high reflectivitysurface as unusable for the second frame, based on the second FET, e.g.,similarly to the identifying stages of method 2400.

It is noted that the high reflectivity surface may be smaller than thelow reflectivity surfaces, and may be surrounded by the low reflectivitysurfaces on all sides, but this is not necessarily so. The highreflectivity surface may correspond in size (e.g., angular size) to asingle PS, to less than one PS, but may also correspond in size toseveral PSs. The difference between the high reflectivity level and thelow reflectivity level may vary. For example, the low reflectivitysurfaces may have reflectivity of between 0 and 15 percent, while thehigh reflectivity surface may be reflectivity of between 80 and 100%. Inanother example, the low reflectivity surfaces may have reflectivity ofbetween 50 and 55 percent, while the high reflectivity surface may bereflectivity of between 65 and 70%. For example, the minimalreflectivity of the high reflectivity surface may be ×2, ×3, ×5, ×10, or×100 of the maximal reflectivity of the low reflectivity surface.Optionally, the high reflectivity surface has reflectivity of more than95% at the spectral range detectable by the PSs (e.g., a white surface),and the low reflectivity surfaces have reflectivity of less than 5% atthe spectral range detectable by the PSs (e.g., black surfaces). It isnoted that as discussed above, a FET may correspond to a fragmented spanof time (e.g., corresponding to several illumination pulses) or to asingle continuous span of time.

It is noted that optionally, the amount light signal levels arrivingfrom the high reflectivity surface to the relevant PS in the first FETand in the second FET may be similar. This may be achieved by filteringof incoming light, by changing an f-number of detection optics 3670correspondingly (e.g. increasing FET by a factor q while increasing thef-number by a factor of q). Optionally, a first exposure value (EV) ofthe PDA during capturing of the first frame information is less than 1%different than a second EV of the PDA during capturing of the secondframe information. Optionally, the difference in FET is the only maindifference between operational conditions between the first frame andthe second frame.

Assessing of temperature of the PDA to calibrate the usability model todifferent levels of dark current was discussed above. Optionally,processor 3620 may be further configured to: (a) process the detectionsignals reflected from the object for determining a first temperatureassessment of the photodetection array during the capturing of the firstframe information and a second temperature assessment of thephotodetection array during the capturing of the first frameinformation, and (b) determine to discard detection resultscorresponding to the high reflectivity surface based on the second FETand on the second temperature assessment.

FIG. 29 is a flow chart illustrating method 3700 for generating imageinformation based on data of a PDA, in accordance with examples of thepresently disclosed subject matter. Referring to the examples set forthwith respect to the previous drawings, it is noted that method 3700 mayoptionally be executed by system 3600. Any variation discussed abovewith respect to system 3600 may be applied to method 3700, mutatismutandis. Especially, method 3700 (and at least stages 3710, 3720, 3730and 3740 thereof) may be executed by processor 3620.

Stage 3710 includes receiving from a PDA first frame information of ablack target that includes a white area, indicative of light intensitiesof different parts of the target detected by the PDA during a first FET.It is noted that the white area may be replaced by a bright area (orother highly reflective area). For example, any area whose reflectivityis higher than 50% may be used instead. It is noted that the blacktarget may be replaced by a dark area (or other slightly reflectivearea). For example, any target whose reflectivity is lower than 10% maybe used instead.

Stage 3720 includes processing the first frame information based on thefirst FET to provide a first image that includes a bright regionsurrounded by a dark background. Optionally, stage 3720 may beimplemented using any of the image generation processes discussed abovewith respect to any of stages 2406, 2414, and 2422 of method 2400.

Stage 3730 includes receiving from the PDA second frame information ofthe black target that includes the white area, indicative lightintensities of the different parts of the target detected by the PDAduring a second FET which is longer than the first FET.

Stage 3740 includes processing the second frame information based on thesecond FET to provide a second image that includes a dark backgroundwithout a bright region. Optionally, stage 3740 may be implemented usingany of the image generation processes discussed above with respect toany of stages 2406, 2414, and 2422 of method 2400, and the precedingstages of identifying groups of usable and unusable PSs.

Regarding the order of execution of method 3700, stage 3720 is executedafter stage 3710, and stage 3740 is executed after stage 3730. Otherthan that, any suitable order of the stages may be used. Method 3700 mayalso optionally include capturing the first frame information and/or thesecond frame information via a PDA.

Optionally, the receiving of the second frame information may bepreceded by determining, after receiving the first frame information,the second FET which is longer than the first FET. Optionally, theprocessing of the second frame information may include discardingdetected light intensity information of the white area based on thesecond FET, and determining a dark color an at least one correspondingpixel of the second image in response to detected light intensities ofneighboring areas of the second frame information. Optionally, theprocessing of the second frame information may include identifying atleast one PS which detects light from the white area as unusable for thesecond frame, based on the second FET. Optionally, a first exposurevalue (EV) of the PDA during capturing of the first frame informationmay be less than 1% different than a second EV of the PDA duringcapturing of the second frame information.

Optionally, during the first frame exposure time dark currentaccumulation on a PS associated with the low reflectivity data leaves ausable dynamic range for the PS, and during the second frame exposuretime dark current accumulation on that PS leaves an insufficient dynamicrange for the PS. In such a case, the PS corresponding to the highreflectivity area cannot be used for image generation in the secondimage, and replacement color value can be calculated to replace themissing detection level.

A non-transitory computer-readable medium is provided for generatingimage information based on data of a PDA, including instructions storedthereon, that when executed on a processor, perform the steps of: (a)receiving from a PDA first frame information of a black target thatincludes a white area, indicative of light intensities of differentparts of the target detected by the PDA during a first FET; (b)processing the first frame information based on the first FET to providea first image that includes a bright region surrounded by a darkbackground; (c) receiving from the PDA second frame information of theblack target that includes the white area, indicative light intensitiesof the different parts of the target detected by the PDA during a secondFET which is longer than the first FET; (d) processing the second frameinformation based on the second FET to provide a second image thatincludes a dark background without a bright region.

The non-transitory computer-readable medium of the previous paragraphmay include additional instructions stored thereon, that when executedon a processor, perform any other step or variation discussed above withrespect to method 3700.

In the disclosure above, multiple systems, methods, and computer codeproducts where described, as well as ways of utilizing them toelectro-optically capture and generate high quality images. Especially,such systems, methods, and computer code products may be utilized togenerate high quality SWIR images (or other SWIR sensing data) in thepresence of high PDs dark current. Such PDs may be Ge PDs, but not onall occasions are. Some ways of using such systems, methods, andcomputer program products in a synergetic way were discussed above, andmany others are possible and are considered as part of the innovativesubject matter of the present disclosure. Any system discussed above mayincorporate any one or more components from any one or more of the othersystems discussed above, to achieve higher quality results, to achievesimilar result in a more effective or cost effective way, or for anyother reason. Likewise, any of the methods discussed above mayincorporate any one or more stages from any one or more of the othermethods discussed above, to achieve higher quality results, to achievesimilar result in a more effective or cost effective way, or for anyother reason.

In the paragraphs below, few non-limiting examples of such combinationsare provided, to demonstrate some of the possible synergies.

For example, imaging systems 100, 100′ and 100″, in which theintegration time is sufficiently short to overcome excessive effect ofdark current noise, may implement PDDs such as PDDs 1300, 1300′, 1600,1600′, 1700, 1800 to be included in receiver 110 to reduce the timeinvariant (direct current, DC) parts of the dark noise. This way, thecapacitance of the PSs is not overwhelmed by the time invariant parts ofthe dark current which are not accumulated in the detection signal, andthe noise of the dark current does not overshadow the detection signal.Implementing any of PDDs 1300, 1300′, 1600, 1600′, 1700, 1800 in any ofimaging systems 100, 100′ and 100″ may be used to extend the frameexposure time to a noticeable degree (because the DC part of the darkcurrent is not accumulated in the capacitance), while still detecting ameaningful signal.

For example, imaging systems 100, 100′ and 100″, in which theintegration time is set sufficiently short to overcome excessive effectof dark current noise, may implement any one or more of methods 2400,2500 and 3500 to determine which PSs are usable at that frame exposuretime, and possibly to reduce the frame exposure time (which correspondsto the integration time) even further to ascertain that a sufficientnumber of PSs are usable. Likewise, the expected ratio between thereadout noise and the expected accumulated dark current noise level at agiven FET and the expected usability of the different PS in such a FETmay be used by the controller to set a balance between the quality ofthe detected signal, the amount of usable pixels, and the illuminationlevel required from the light source (e.g., laser 600). The usabilitymodel at different FETs may also be used to determine the distanceranging of the gated images generated by imaging system 100, 100′ and100″, when applicable. Further incorporating any of PDDs 1300, 1300′,1600, 1600′, 1700, 1800 as the sensor of such imaging system would addthe benefits discussed in the previous paragraph.

For example, any one or more of methods 2400, 2500 and 3500 may beimplemented by system 1900 (or by any EO system that includes any ofPDDs 1300, 1300′, 1600, 1600′, 1700, 1800). The reduction of the effectsof dark current accumulation as discussed with respect to system 1900(or any of the PDDs mentioned) allow utilization of longer FETs.Implementing any of methods may be used to facilitate the longerpossible FETs, because determining which PSs are temporarily unusable ina relatively long FET enable system 1900 (or another EO system with oneof the PDDs mentioned) to ignore such PSs, and optionally to replacetheir detection output with data of neighboring PSs.

Some stages of the aforementioned methods may also be implemented in acomputer program for running on a computer system, at least includingcode portions for performing steps of a the relevant method when run ona programmable apparatus, such as a computer system or enabling aprogrammable apparatus to perform functions of a device or systemaccording to the disclosure. Such methods may also be implemented in acomputer program for running on a computer system, at least includingcode portions that make a computer execute the steps of a methodaccording to the disclosure.

A computer program is a list of instructions such as a particularapplication program and/or an operating system. The computer program mayfor instance include one or more of: a subroutine, a function, aprocedure, a method, an implementation, an executable application, anapplet, a servlet, a source code, code, a shared library/dynamic loadlibrary and/or other sequence of instructions designed for execution ona computer system.

The computer program may be stored internally on a non-transitorycomputer readable medium. All or some of the computer program may beprovided on computer readable media permanently, removably or remotelycoupled to an information processing system. The computer readable mediamay include, for example and without limitation, any number of thefollowing: magnetic storage media including disk and tape storage media;optical storage media such as compact disk media (e.g., CD-ROM, CD-R,etc.) and digital video disk storage media; nonvolatile memory storagemedia including semiconductor-based memory units such as FLASH memory,EEPROM, EPROM, ROM; ferromagnetic digital memories; MRAM; volatilestorage media including registers, buffers or caches, main memory, RAM,etc.

A computer process typically includes an executing (running) program orportion of a program, current program values and state information, andthe resources used by the operating system to manage the execution ofthe process. An operating system (OS) is the software that manages thesharing of the resources of a computer and provides programmers with aninterface used to access those resources. An operating system processessystem data and user input, and responds by allocating and managingtasks and internal system resources as a service to users and programsof the system.

The computer system may for instance include at least one processingunit, associated memory and a number of input/output (I/O) devices. Whenexecuting the computer program, the computer system processesinformation according to the computer program and produces resultantoutput information via I/O devices.

The connections as discussed herein may be any type of connectionsuitable to transfer signals from or to the respective nodes, units ordevices, for example via intermediate devices. Accordingly, unlessimplied or stated otherwise, the connections may for example be directconnections or indirect connections. The connections may be illustratedor described in reference to being a single connection, a plurality ofconnections, unidirectional connections, or bidirectional connections.However, different embodiments may vary the implementation of theconnections. For example, separate unidirectional connections may beused rather than bidirectional connections and vice versa. Also,plurality of connections may be replaced with a single connection thattransfers multiple signals serially or in a time multiplexed manner.Likewise, single connections carrying multiple signals may be separatedout into various different connections carrying subsets of thesesignals. Therefore, many options exist for transferring signals.

Optionally, the illustrated examples may be implemented as circuitrylocated on a single integrated circuit or within a same device.Alternatively, the examples may be implemented as any number of separateintegrated circuits or separate devices interconnected with each otherin a suitable manner. Optionally, suitable parts of the methods may beimplemented as soft or code representations of physical circuitry or oflogical representations convertible into physical circuitry, such as ina hardware description language of any appropriate type.

Other modifications, variations and alternatives are also possible. Thespecifications and drawings are, accordingly, to be regarded in anillustrative rather than in a restrictive sense. While certain featuresof the disclosure have been illustrated and described herein, manymodifications, substitutions, changes, and equivalents will now occur tothose of ordinary skill in the art. It is, therefore, to be understoodthat the appended claims are intended to cover all such modificationsand changes as fall within the true spirit of the disclosure. It will beappreciated that the embodiments described above are cited by way ofexample, and various features thereof and combinations of these featurescan be varied and modified. While various embodiments have been shownand described, it will be understood that there is no intent to limitthe disclosure by such disclosure, but rather, it is intended to coverall modifications and alternate constructions falling within the scopeof the disclosure, as defined in the appended claims.

In the claims or specification of the present application, unlessotherwise stated, adjectives such as “substantially” and “about”modifying a condition or relationship characteristic of a feature orfeatures of an embodiment, are understood to mean that the condition orcharacteristic is defined to within tolerances that are acceptable foroperation of the embodiment for an application for which it is intended.It should be understood that where the claims or specification refer to“a” or “an” element, such reference is not to be construed as therebeing only one of that element.

All patent applications, white papers and other publicly available datapublished by the assignee of the present disclosure and/or by TriEyeLTD. of Tel Aviv, Israel are incorporated herein by reference in theirentirety. No reference mentioned herein is admitted to be prior art.

What is claimed is:
 1. A passively Q-switched (P-QS) laser, comprising:a gain medium comprising a gain medium crystalline (GMC) material thatincludes a ceramic neodymium-doped yttrium aluminum garnet (Nd:YAG); asaturable absorber (SA) rigidly coupled to the gain medium, the SAcomprising a ceramic saturable absorber crystalline (SAC) materialselected from the group of doped ceramic materials consisting of athree-valence vanadium-doped yttrium aluminum garnet (V³⁺:YAG) andtwo-valence Cobalt-doped crystalline materials; and an optical cavitywithin which the gain medium and the SA are positioned, the opticalcavity including a high reflectivity mirror and an output coupler. 2.The P-QS laser of claim 1, further comprising undoped YAG in addition tothe gain medium and to the SA, for preventing heat from accumulating inan absorptive region of the gain medium.
 3. The P-QS laser of claim 2,wherein the undoped YAG is shaped as a cylinder encircling the gainmedium and the SA.
 4. The P-QS laser of claim 1, wherein at least one ofthe GMC material and the SAC material is polycrystalline.
 5. The P-QSlaser of claim 1, wherein both the GMC and SAC materials arepolycrystalline.
 6. The P-QS laser of claim 1, wherein the highreflectivity mirror and the output coupler are rigidly coupled to thegain medium and the SA such that the P-QS laser is a monolithicmicrochip P-QS laser.
 7. The P-QS laser of claim 1, wherein the GMCmaterial is neodymium-doped yttrium orthovanadate (Nd:YVO₄).
 8. The P-QSlaser of claim 1, wherein the SAC material is cobalt-doped Spinel(Co²⁺:MgAl₂O₄).
 9. The P-QS laser of claim 1, wherein the SAC materialis Co²⁺:YAG.
 10. The P-QS laser of claim 1, wherein the SAC material iscobalt-doped Zinc selenide (Co²⁺:ZnSe).
 11. The P-QS laser of claim 1,wherein the GMC material is a ceramic cobalt-doped crystalline material.12. The P-QS laser of claim 1, wherein the gain medium and the SA areimplemented on a single piece of crystalline material doped withneodymium and at least one other material.
 13. The P-QS laser of claim1, wherein an initial transmission (To) of the SA is between 78% and82%.
 14. An electrooptical system, comprising: the P-QS laser of claim1, configured to illuminate a target, and a sensor configured to senseradiation reflected from the illuminated target and convert thereflected illumination into image data.
 15. The electrooptical system ofclaim 14, further comprising a processor operable to process the imagedata provided by the sensor for determining a presence of an object in afield of view of the electrooptical system.
 16. A method formanufacturing parts for a passively Q-switched (P-QS) laser, comprising:inserting at least one first powder into a first mold; compacting the atleast one first powder in the first mold to yield a first green body;inserting at least one second powder different than the at least onefirst powder into a second mold; compacting the at least one secondpowder in the second mold, thereby yielding a second green body; heatingthe first green body to yield a first crystalline material; heating thesecond green body to yield a second crystalline material; and couplingthe second crystalline material to the first crystalline material,wherein one of the first crystalline material and the second crystallinematerial is a neodymium-doped crystalline material and is a gain mediumfor the P-QS laser, wherein the other of the first crystalline materialand the second crystalline material is a saturable absorber (SA) for theP-QS laser and is a material selected from the group consisting of aneodymium-doped crystalline material and a doped crystalline material,wherein the doped crystalline material is selected from the groupconsisting of a three-valence vanadium-doped yttrium aluminum garnet(V³⁺:YAG) and a cobalt-doped crystalline material, and wherein at leastone of the gain medium and the SA is a ceramic crystalline material. 17.The method of claim 16, wherein the first mold is different than thesecond mold.
 18. The method of claim 16, wherein the first mold and thesecond mold are the same mold.
 19. The method of claim 16, wherein theheating of the first green body precedes the compacting of the at leastone second powder and wherein both the gain medium and the SA arepolycrystalline materials.
 20. The method of claim 17, wherein theheating of the first green body precedes the compacting of the at leastone second powder and wherein both the gain medium and the SA arepolycrystalline materials.
 21. The method of claim 18, wherein theheating of the first green body precedes the compacting of the at leastone second powder and wherein both the gain medium and the SA arepolycrystalline materials.
 22. The method of claim 16, wherein theheating of first green body and the heating of the second green bodycomprise concurrent heating of the first green body and the second greenbody in a single oven and wherein both the gain medium and the SA arepolycrystalline materials.
 23. The method of claim 17, wherein theheating of first green body and the heating of the second green bodycomprise concurrent heating of the first green body and the second greenbody in a single oven and wherein both the gain medium and the SA arepolycrystalline materials.
 24. The method of claim 18, wherein theheating of first green body and the heating of the second green bodycomprise concurrent heating of the first green body and the second greenbody in a single oven and wherein both the gain medium and the SA arepolycrystalline materials.
 25. The method of claim 16, wherein thecoupling is a result of the heating of the single oven.
 26. The methodof claim 17, wherein the coupling is a result of the heating of thesingle oven.
 27. The method of claim 18, wherein the coupling is aresult of the heating of the single oven.